The United States and North Korea began another bilateral meeting in Beijing Thursday morning as they attempt to narrow their differences in talks aimed at denuclearizing the Korean peninsula, the Xinhua News Agency said.

It will be the third contact this week between the two sides.

The French news agency AFP quoted witnesses as saying a North Korean convoy of cars entered the Diaoyutai State Guest House just before 9 am with the American delegation following soon after.

It quoted the source as saying other parties to the six-nation talks remained at their hotels to give the United States and North Korea space for talks described by Russian officials Wednesday as crucial to the success of the fourth round of negotiations.

The six-party talks, entering their third day, also involve South Korea, Russia, Japan and host nation China.

U.S. envoy Christopher Hill first met with his North Korean counterpart Kim Kye-gwan in a 75-minute meeting on Monday ahead of the official start of the multinational talks.

They met again Tuesday in "long" discussions that the Americans described as "good" and "businesslike."

But reports say Washington and Pyongyang are still far apart on proposals for ending the crisis.

North Korea reacted coolly to a U.S. offer dating back to June 2004 to provide security guarantees and South Korean aid in return for the North agreeing to dismantle -- not just freeze -- its nuclear programs in a verifiable way.

Pyongyang has insisted on security guarantees and aid pledges before it moves to scrap its weapons program, and a senior U.S. official told reporters the North Koreans had objected to the proposal that they should move first.

"They were not entirely satisfied by it and had some concerns about the sequencing of obligations, feeling their obligations were frontloaded and the obligations of the other parties were backloaded," the U.S. official told a briefing after the second day of talks.

The U.S. official said the elements laid out in the June 2004 proposal remained the basis of Washington's position but hinted that there might be some flexibility on timing.

Participants were now focusing on agreeing some form of statement as a framework, "a set of agreed principles on the basis of which we can narrow the scope of issues and lay out an eventual schedule for negotiation of an overall agreement," he added.

A South Korean official said Seoul had proposed that the six adopt a joint document setting out two "pillars" or matching promises without specifying the sequence of events -- which might help bridge the gulf between Washington and Pyongyang.

North Korea staked out a tough position on Wednesday on the second day of talks, demanding U.S. concessions as the other five outlined proposals for resolving the crisis.

Pyongyang demanded Washington remove nuclear weapons from the Korean peninsula. The United States, which keeps more than 30,000 troops in South Korea, says it no longer has such weapons in the country.