Toronto: US President Barack Obama demanded the United Nations condemn North Korea for its "unacceptable" and "belligerent behaviour" and said China must stop turning a blind eye to its neighbour.
"Our main focus right now is in the UN Security Council making sure that there is a crystal clear acknowledgement that North Korea engaged in belligerent behaviour that is unacceptable to the international community," Obama told a press conference on Sunday.
He recalled that a multinational investigation had found that Pyongyang was to blame for the sinking of a South Korean warship in March, in which 46 sailors died.
The US and Seoul have led a push for a UN censure of Pyongyang for the sinking of the 1,2000-tonne Cheonan, triggering threats of military reprisals from the isolated Stalinist state.
Obama said he believed South Korean President Lee Myung-Bak "has shown extraordinary restraint given these circumstances”.
"It is absolutely critical that the international community rally behind him and send a clear message to North Korea that this kind of behaviour is unacceptable," he added.
Obama met with Lee on the sidelines of G20 talks in the eastern Canadian city of Toronto, and vowed that Washington stood behind him.
He also held talks with Chinese President Hu Jintao, and said he had been "blunt" with him on the issue of North Korea.
Beijing is a close ally of Pyongyang`s and has been reluctant to endorse a UN condemnation over the ship sinking until it has assessed the evidence for itself.