The International criminal court's prosecutor is studying alleged war crimes by North Korea in the South's territory, he said today.
Luis Moreno-Ocampo's office said in a statement that it had opened a preliminary examination to evaluate whether the incidents constituted war crimes under the court's jurisdiction, after receiving the allegations.
They include last month's artillery attack, in which two civilians and two soldiers died, and the sinking of a warship this spring, resulting in the deaths of 46 sailors. Pyongyang denied involvement in that case, but international investigators said a northern torpedo was responsible.
The announcement comes amid renewed diplomatic efforts to reduce tensions on the peninsula, which are at their highest point for years, following the bombardment of Yeonpyeong island. South Korea today began fresh military exercises at sites including an area close to the disputed Yellow Sea border – despite military warnings from the north.
Chinese state media said president Hu Jintao told Barack Obama that Beijing feared the situation could spiral out of control in a telephone call late last night.
The US secretary of state Hillary Clinton will later today host talks with her Japanese and South Korean counterparts to discuss the North's attack on Yeonpyeong island two weeks ago. They have said they will discuss China's proposal for an emergency meeting of the six countries involved in the stalled aid-for-denuclearisation talks, which they have so far snubbed.
Beijing is under pressure from the US and others to rein in its ally. It has not criticised the North for the attack, merely calling on both sides to show restraint.
"Especially with the present situation, if not dealt with properly, tensions could well rise on the Korean peninsula or spin out of control, which would not be in anyone's interest," Xinhua news agency paraphrased Hu as telling Obama.
He added: "The most pressing task at present is to calmly deal with the situation."
In a statement, the White House said Obama had urged China to work with the US and others to "send a clear message to North Korea that its provocations are unacceptable".
It added that the two men also discussed Iran in the phone call made by Obama.
The South's military said the drills that begin today will take place at 29 locations including Daecheong island, in the western sea near the disputed northern limit line, which the North has never accepted. The area saw a deadly naval skirmish last year.
Pyongyang has said the manoeuvres show Seoul is "hell-bent" on war. It blamed similar live-fire exercises for its artillery attack on Yeonpyeong island, in which two civilians and two soldiers from the South died.
The state news agency KCNA said yesterday that the South's "frantic provocations ... are rapidly driving the situation on the Korean peninsula to an uncontrollable extreme phase. No one can predict to what extent the situation will deteriorate in the future."
Although it often issues such warnings before military training by the South, they are being taken more seriously in light of the Yeonpyeong shelling.
But Reuters reported that an increasing number of residents have returned to the island, suggesting they do not expect the situation to escalate.
Seoul has taken an increasingly tough line on its neighbour in public, as domestic criticism grows over the government's handling of the attack.
But others have argued that the government's tougher stance towards the North have alienated Pyongyang and contributed to the current tensions.
Relations on the peninsula deteriorated rapidly after Lee Myung-bak became president of the South and halted the generous flow of aid that the North had enjoyed under his predecessors' "sunshine policy".
