Hundreds of rebel fighters pushed into the centre of the Libyan capital, Tripoli, late on Sunday as their battle to overthrow the 42-year rule of Muammar Gaddafi moved closer to ending in victory.
Rebels waved opposition flags and fired guns into the air in jubilation after reaching Tripoli's central Green Square, the symbolic heart of the city, in the early hours of Monday morning.
Delighted residents were seen pouring into the streets to celebrate and greet the rebel fighters as they advanced through the suburbs towards the centre.
The prosecutor of the international criminal court said one of Gaddafi's sons, Saif al-Islam, who has been indicted along with his father on crimes against humanity charges had been detained.
The head of the rebel Transitional National Council, Mustafa Abd el-Jalil said that his fighters who had detained Saif al-Islam had been given instructions to "treat him well".
There were also reports that Gaddafi's eldest son, Mohammed, and the presidential guard had surrendered but Gaddafi's Bab al-Aziziya compound was still under the control of the regime.
On Sunday night Barack Obama called on Gaddafi to recognise that his rule is at an end and to immediately resign in order to save Libya from enduring further bloodshed.
"The momentum against the Gaddafi regime has reached a tipping point," the US president said in a statement. "Tripoli is slipping from the grasp of a tyrant. The Gaddafi regime is showing signs of collapsing. The people of Libya are showing that the universal pursuit of dignity and freedom is far stronger than the iron fist of a dictator."
"The surest way for the bloodshed to end is simple: Muammar Gaddafi and his regime need to recognise that their rule has come to an end. Gaddafi needs to acknowledge the reality that he no longer controls Libya. He needs to relinquish power once and for all."
Obama also called on the Transitional National Council to ensure that civilian lives are protected and pursue "a transition to democracy that is just and inclusive for all of the people of Libya".
"A season of conflict must lead to one of peace," he said.
As crowds gathered in Tripoli and the rebel-held city of Misrata, Gaddafi staged a dramatic late-night appeal for help.
Speaking on state television via audiolink, for the second time on Sunday, the dictator sounded more measured than in previous, emotionally charged speeches. He said to the Libyan people: "There are criminals, they are coming to destroy Tripoli. They are coming to steal our oil.
"Now it [Tripoli] is in ruins. They are coming, they are destroying it. Come out of your houses and fight these betrayers. Hurry up, hurry up, families and tribes, go to Tripoli. Call the tribes to go to Tripoli."
Libyan information ministry spokesman Moussa Ibrahim also insisted that Gaddafi forces would stand and fight. He said: "We are still very strong. We have thousands and thousands of fighters who have nowhere to go but to fight.
"Nato has intensified its attacks on and around Tripoli, giving immediate and direct support for the rebels' forces to advance into a peaceful capital of this great nation and the death toll is beyond imagination."
In an attempt to try to avoid a heavy battle in the city centre, Abd el-Jalil said the rebel fighters would halt their offensive if Gaddafi announced his departure, adding that they would give Gaddafi and his sons safe passage out of the country.
Nato said on Sunday the situation was "very fluid". "We can see that the regime is crumbling, and the sooner Gaddafi realises he cannot win this war against his own people, the better," Nato spokeswoman Oana Lungescu said. "He's the one who's responsible for starting the conflict and he should spare his people further bloodshed," she added.
Britain called on Gaddafi to stand down to save his people from further suffering. Downing Street said it was clear that the "end is near" for the Libyan leader.
"It is clear from the scenes we are witnessing in Tripoli that the end is near for Gaddafi," No 10 said. "He has committed appalling crimes against the people of Libya and he must go now to avoid any further suffering for his own people."
Earlier Muammar Gaddafi called for supporters from across Libya to help him defend the capital, with rebel forces then already in control of parts and massing on its western outskirts for a decisive assault.
As Libya's dictator vowed that he would not be forced into exile. "We will fight to the last drop of blood," he said. "We will never give up."
He warned of a furious fight ahead, with the remnants of the Libyan army and well-armed vigilantes bracing for urban warfare. As government forces went into full retreat towards the capital from the road west to Zawiya and from al-Aziziya, 30 miles (45km) to the south, Gaddafi again called the rebels "rats".
"All the patriots of Libya, come to defend the capital," he said, adding that he feared "Tripoli would burn."
The rebels had advanced rapidly on Tripoli during the day, seizing the town of Jadda'im and an outpost called Bridge 27, 17 miles from the centre of the capital, as they pushed east.
Gaddafi had maintained a strong base of support in Tripoli, but neither its size nor resilience were tested during the six months of civil war, in which government forces there successfully crushed dissent and retained control.
In the capital on Sunday afternoon, one of the largest military bases was overrun by rebel forces, who freed up to 5,000 people imprisoned by the regime and then swung open the doors of the armoury, allowing thousands of rebel supporters to seize weapons. Reports from the Mais base revealed residents were celebrating wildly. Misrata military council confirmed that units of Misrata rebels made a beach landing near Tripoli, to deliver weapons and ammunition to rebels.
Observers inside the capital said barricades had been erected in some suburbs and soldiers had taken up defensive positions. Weapons and ammunition were distributed to loyalists earlier in the uprising, raising the prospect of prolonged guerrilla warfare within the city although as the rebels moved through the capital there was no sign of armed resistance.
Gaddafi's compound in the centre of Tripoli was bombed again by Nato jets early on Sunday, and only several miles away uprisings were reported to be underway in the suburbs of Tajoura and Fashloum. Sustained gunfire from both areas on Saturday night appeared to mark the first time that rebel movements in either area had been able to gain momentum since anti-regime protests erupted on 17 February.
Opposition troops were attempting to consolidate gains in the capital by trying to seize control of a disused airfield on the city's eastern edges in a bid to establish a supply line. Their rapid advances of the past week have already shut off a government supply line to the Tunisian border.
Gaddafi has spent much of the past five months sleeping in Tripoli hospitals, or in rooms in the city's largely empty five-star hotels. His other military forces have been severely weakened during months of fighting and more than 1,000 bombing raids by Nato jets, which have focused heavily on weapons stockpiles and command and control centres.
Even if Gaddafi backed down, he has few options inside or out of Libya. The international criminal court has issued warrants for him and key regime officials, which means he is at risk if he travels to any country that recognises the jurisdiction of the ICC.
"We remember our dead now," said Zaynab Shawaid, of the Shaheed (Martys) women, a self-help group of women. "We are proud of our dead. There are celebrations yes, and the memory of the dead will be with us as we build a new Libya."
Rebels around Misrata had orders to be on alert, after a day of fighting south of the neighbouring town of Zlitan that left two rebel dead and 14 wounded.
"I feel good but I can't believe it yet," said rebel fighter Abdullah Maiteeg, 24, of Misrata's Shaheed brigade, standing watching the celebrations in Misrata's ruined Tripoli Street. "Right now I don't want to celebrate, I'm thinking of my friends, Mohammed Algajiji and Alaa Khsheem, they died for this. I don't want to celebrate until I see the G-dog [Gaddafi] his head separated from his body."