The green wheat fields shimmer in the late afternoon light as the wind slowly starts to pick up. A cloud of dust drifts by. This is good, says Abu Abdu, a farmer from the village of Telminnes, located deep in the south of Syria's Idlib province. Prior to the war, the evening wind had been an annoyance for the dust it kicked up. But these days, it is windless nights that people in the area despise. That's when air force helicopters come and the gas attacks take place. Often, they circle over the city before dropping their cargo.

Usually, there is no big bang, just the sound of a minor detonation, sometimes even just the thud of an impact. Death comes quietly, as it did on the evening of April 21 in Telminnes.

That's the evening a bomb landed near Abu Abdu's garden. The farmer says the explosion was a quiet one. "I thought the point of impact was far away," he recalls. The bomb, which carried a small amount of explosives and a gas cylinder, fell close by -- so close that Abu Abdu could already see the cloud before he had the chance to flee. "Yellow vapor rose, it smelled strongly of chlorine and it burned like fire. I could no longer speak or breathe," he says. Neighbors took him to a makeshift hospital where he was treated with oxygen and an anticonvulsant. "Hours later, I could still barely move my arms, I was coughing up blood and every breath I took was hellish."

Between 200 and 300 people went to hospital in Telminnes that night, suffering from burns in their respiratory passages, difficulty breathing and eye irritation. None showed signs of external injuries. Abu Abdu and others were then transferred to hospitals in the north. The patients suffering the worst injuries were taken to Turkey, where two children later died.

Abu Abdu has since returned home, but he still suffers from coughing fits. Every night he hopes the wind will blow; the regime, he says, won't risk a chlorine gas attack in such conditions. "Maybe they're afraid for their soldiers in Wadi Deif," he says. The province's largest army base is located only a few kilometers south of Telminnes.

Assad Doesn't Have to Hand Over Chlorine

Although Damascus has turned over 92.5 percent of its chemical weapons stockpile, including sarin, as agreed, it continues to deploy poison gas against the Syrian people. Given chlorine's use in everyday products, it isn't included in the list of weapons the regime has agreed to place under international control. Its deployment against humans is nonetheless prohibited under the Chemical Weapons Convention, of which Syria is a signatory.

At least 10 chlorine gas attacks have been carried out since April 10 in the border areas of the Idlib and Hama provinces, including one in Telminnes, three in Al-Tamana'a and six in the small city Kfar Zeita and the surrounding area. The hilly, rural region is a battlefield that has been largely overlooked by the public. It's difficult to reach, there are no major cities in the area and it has been the scene of bitter fighting for minimal territorial gain. During the past two months, the regime has lost control of strategically important villages here, and rebels have also blocked the highway between Hama and Aleppo. Now it appears that Damascus is seeking to gain the upper hand through the use of chlorine gas.

The nature of the attacks appears to be the same in each instance, with witnesses saying they involve barrel bombs being dropped from helicopters. They are cheaply made constructions, welded together by the military. They are then filled with explosives and metal shrapnel -- or chlorine.

On April 12, Syrian state television reported that the al-Qaida-aligned al-Nusra Front had detonated containers with chlorine. But the regime also made similar claims after the sarin attacks that occurred last year. And research conducted by SPIEGEL refutes this new claim. A SPIEGEL team succeeded in visiting all three sites of the attacks and spoke to people who suffered injuries, witnesses and doctors at the scene and also investigated impact craters and the remains of projectiles. Journalists with SPIEGEL were the first foreign reporters to reach the site.

Our journalists determined that the village of Al-Tamana'a in the Idlib province was also targeted, with over 100 injured being taken to hospital in the wake of chlorine gas attacks on the nights of April 12 and 18. All the victims suffered from the same symptoms as those in Telminnes: trouble breathing, fits of suffocation, coughing up of blood, redness of the eyes and a strong flow of spittle. "On April 18, we only took the worst cases to the larger hospitals," says one medic. "Then we had to evacuate everyone when the gas reached the ward and the smell of chlorine got stronger and stronger." He says five people died.

'Perhaps It Was a Test'

The worst attacks targeted Kfar Zeita, the small city from which the first reports about the chlorine gas injuries originated. Before the war, 25,000 people lived here, but only one-tenth of the population remains. The rest have either fled or died. During the drive to the city, you pass by ghost towns, burned out tanks, dirt roads and a completely desolate stretch of highway. Only a few kilometers separate the city from the regime's military positions.

The first chlorine bomb was dropped on April 10, but nobody was injured in the incident. "Perhaps it was a test," says Abdullah Darwish, a doctor at one of the two hospitals in the city that are still operational. The next night, a second barrel bomb was dropped about 400 meters away from the clinic. This time it exploded with a large detonation. The doctor says he saw it unleash a yellow cloud that quickly fell on local homes.

Only a few minutes later, the first of over 100 victims turned up at the hospital. "The first victim, a refugee, died after suffering from head injuries from the attack, but not from the gas" he says. The man had come from Morek, a neighboring town that has been the site of heavy fighting. "The people are fleeing from the bombs, but where too? To Kfar Zeita," the doctor says. And once they get there they are getting bombed again. It's like going from one hell to the next. The man's daughter died four days later -- her respiratory passages had been burned by gas.

On April 12, 16, 18 and 26, chlorine gas bombs fell on Kfar Zeita and the surrounding area. One bomb injured five people, another 50. "It appears as though we are being used a guinea pigs for the regime's new weapons," says Darwish. "They also used Russian rocket launchers with cluster munitions for the first time in Kfar Zeita."

The surgeon, a chain smoker with a Jack Nicholson-like grin, knows what he's talking about. He transformed the private clinic into one of the best hospitals in the region. "We can do open-heart surgery and we have up to 10 doctors here, including orthopedists, cardiologists and surgeons," he says. He adds that the hospital is provided with support from the US-based Syrian American Medical Society and from the British government.

Further Indications Regime Behind Attacks

But it could all end with the blink of an eye. "The army knows exactly where we are," he says. "When we hear the noise of the rotors, we look up to see where the bombs fall. So far, they have missed us 16 times. We're continuing with our work." It appears that the wind has saved them, as well as the pilots' own fear. Indeed, they fly at a height of four kilometers (2.5 miles) in order to avoid getting shot down by the rebels, but this also makes the dropping of bombs very imprecise.

The attack on April 18 did nearly strike the city's second hospital, whose staff are provided with supplies by Abdullah Darwish's colleagues. Neither of the two barrel bombs dropped exploded; they were torn open on impact, with the gas seeping out more slowly, which may have saved lives. It is this stroke of luck that also provides the strongest indication yet of the perpetrator of the attacks.

The bombs, bent out of shape on impact, all have an almost one-centimeter thick steel casing. Inside are cylinders of a type often used in industrial manufacturing with the engraved initials "CL²" as well as the name of Norinco, the suspected Chinese manufacturer. Cl² is the symbol for chlorine gas. Identical cylinders with the same engraving have been found in other unexploded barrel bombs in Telminnes as well as in bombs that detonated, but were not completely destroyed, near the home of farmer Abu Abdu.

Chlorine gas attacks are difficult to prove. Forensic samples taken by a Syrian doctor that were then analyzed by professional weapons experts commissioned by Britain's Telegraph newspaper, which published its findings  last week, determined high concentrations of chlorine at the impact sites. The problem is that chlorine is also used in bleach or as a disinfectant. Another is that chlorine gas doesn't leave behind the kind of specific chemical signature that can be detected in the decomposition products of sarin. Nonetheless, you would still need a helicopter to drop half-ton bombs from such a high elevation, and Syria's rebels do not have them at their disposal.

There are other indications the regime was the perpetrator, as well, but it isn't possible to confirm them independently. While the rebels don't have any weapons they can use to combat high-flying jets or helicopters, technicians with the Islamist Front, the largest rebel alliance in the north, are able to intercept the radio communications of the pilots and the army. They maintain listening stations scattered every few kilometers in tents, farm yards or under olive trees. The men monitor flight paths and the announcements made over the radio. They also radio in their own warnings about possible attacks.

In addition, they routinely eavesdrop on communications at Wadi Deif, the massive military base near Telminnes, as they did on April 21, the day the two gas bombs were dropped on the city. The rebels claim that a warning was broadcast that day that soldiers should have their gas masks ready. Hours later, they claim regime soldiers celebrated over radio that the "terrorists" in Telminnes were having to dispatch "many ambulances" just now.

The state broadcaster in Damascus continued to report that the al-Nusra Front had been responsible for the gas attacks. A statement from the Foreign Ministry in Moscow also claimed it possessed "trustworty data" indicating that the allegations lodged against the Syrian regime were untrue. The statement dismissed the claims as "anti-Syrian 'chemical' hysteria." However, officials in the United States, France and Britain all said there was evidence of a gas attack. An investigation by the Organization for the Prohibition of Chemical Weapons is expected to clarify the events. Damascus formally agreed to the probe last week, but only in areas that are under the regime's control. Unfortunately, these areas do not include any of the sites of the chlorine gas attacks that have been perpetrated thus far.

No Hope for End of Hostilities

Currently, the regime is prevailing militarily in the middle of the country -- in Homs and around Damascus -- but it is losing towards the periphery, in places like Idlib and Hama in the north and in Daraa in the south. The eastern part of the country has almost entirely slipped out of Damascus' control. In this fourth year of fighting, hopes have expired that 2014 might bring an end to the conflict. Instead, both sides are still digging in their heels. Doctor Abdallah Darwish is left to hope that the next bomb will miss him too. And despite the fact that nearly half the population has fled, Syrian President Bashar Assad still plans to hold June 3 elections to affirm an additional seven-year term as the country's leader. Meanwhile, the rebels continue to fight and religious groups are gaining clout.