The United States, Japan and South Korea (search) have worked out a joint proposal on how to ease tensions over North Korea's nuclear weapons program and will ask China to relay it to the communist North, a senior South Korean official said Saturday.

If Pyongyang (search) accepts the proposal, a second round of six-nation talks on the North Korean nuclear crisis will convene in Beijing, Deputy Foreign Minister Lee Soo-hyuck told South Korean reporters upon returning home from a trip to Washington.

Ahead of the Washington talks, South Korean officials said the proposal would deal with the main sticking point: when the United States should give written security assurances to North Korea. The North wants Washington to issue the assurances simultaneously with a Northern renunciation of its nuclear weapons program, while the United States wants the North to move first.

"The three countries have reached an understanding on the wording of a joint statement and agreed to give it to China," Lee said. "China will send it to Pyongyang and then there will be a response."

"The next few days are crucial. I am neither optimistic nor pessimistic," he added.

He did not give details on the proposal, drawn up in talks with his Japanese counterpart, Mitoji Yabunaka, and U.S. Assistant Secretary of State James Kelly (search). The three are their countries' top negotiators at the nuclear talks, which also include China and Russia.

The six-nation talks had been expected to convene in Beijing on Dec. 17. But officials in Washington and Seoul had indicated that they might be delayed, particularly because of differences over the security assurances.

Since the first round of the six-party talks was held in August in Beijing, North Korea has made demands for concessions -- including the security guarantees -- to be extended simultaneously with a drawdown of its nuclear program instead of after the program has been shut down.

North Korea rejects a U.S. demand that it first renounce its nuclear weapons program, saying it would "rather die" than submit to conditions that amounted to slavery.

China, North Korea's major ally, has taken the lead in informal discussions with North Korea.

In its offer, North Korea said it would declare its willingness to give up nuclear development, allow nuclear inspections, give up missiles exports and finally dismantle its nuclear weapons facilities. In return, it demanded economic and humanitarian aid, security assurances, diplomatic ties and new power plants.

A second round of talks would aim at adopting a declaration outlining a sequence of steps.

The nuclear crisis began in October 2002, when U.S. officials said North Korea admitted having a nuclear weapons program in violation of international agreements.

The United States and its allies suspended oil shipments to the North. North Korea in turn expelled United Nations nuclear inspectors, withdrew from the global nuclear arms-control treaty and said it was building nuclear arms to defend itself from U.S. invasion.