Diplomatic sources in Washington say the United States had proposed replacing the Korean War armistice with a permanent peace mechanism at the second round of six-way nuclear talks.

The sources said Sunday that U.S. Undersecretary of State for East Asian and Pacific Affairs James Kelly made the proposal to North Korea during the six-party talks held in February in Beijing.

Kelly was quoted as saying that establishing a permanent peace mechanism would be the final stage of a three-phase formula the United States had proposed to resolve the North Korean nuclear issue.

The U.S. also proposed opening negotiations to normalize relations with the communist state in addition to signing a peace agreement if Pyongyang would show consistent progress in completely, verifiably and irreversibly dismantling its nuclear programs.

The two Koreas, the United States, China, Russia and Japan are set to hold working-level talks on the North's nuclear issue on May 12 in Beijing.