US President Barack Obama on Wednesday warned that Iran and North Korea would face even deeper isolation if they failed to bring their nuclear programs under international law.

"There is a future of greater opportunity for the people of these nations if their governments meet their obligations. But if they continue down a path that is outside international law, they must be met with greater pressure and isolation," Obama said. "That is what our commitment to peace demands."

Obama has argued that his administration had worked to strengthen treaties and institutions dedicated to the spread of nuclear weapons and needed to hold those nations who flout such regimes accountable.

"The Iranian government cannot demonstrate that its program is peaceful, has not met its obligations, and rejected offers that would provide it with peaceful nuclear power," Obama told the UN General Assembly.

"North Korea has yet to take concrete steps toward abandoning its weapons, and continues belligerent actions against the South."

The president's comments came as the chief nuclear envoys for North and South Korea met in Beijing but failed to reach agreement on reviving nuclear disarmament talks.

North Korea formally abandoned the six-nation forum, a process which began back in 2003 and groups the two Koreas, China, the United States, Japan and Russia, in April 2009.

At the International Atomic Energy Agency general conference in Vienna this week, the United States warned Tehran was creeping "still closer" to producing nuclear weapons-grade uranium.

The UN Security Council has imposed four rounds of sanctions on Iran over its nuclear activities, which the Islamic republic says are peaceful but which Western powers suspect are aimed at developing atomic weapons.