"We are focusing our discussion on what those conditions would be," he said.

Negotiators were addressing the implementation of a September 2005 agreement where North Korea pledged to abandon its nuclear weapons in exchange for security guarantees and aid.

 "Whether we can start implementing the agreement this week, time will tell," Assistant Secretary of State Christopher Hill said Wednesday evening.

He said the talks focused on specific steps toward North Korea's disarmament that the US hoped would happen in a timeframe "a lot shorter than a year."

The North Koreans appeared interested and there were many questions between the sides, Hill said.

Hill declined to release details of US proposals to North Korea, but a news report Wednesday said the Americans had outlined a process in which the North would first freeze its nuclear program, followed by inspections and eventual dismantlement.

Washington would be willing to give North Korea a written security guarantee - a pledge that it would not seek to topple the government by force - as soon as the country allows the return of international nuclear inspectors, South Korea's Yonhap news agency said, citing "diplomatic sources" at the talks.

"We cannot be just optimistic about the situation since this round of talks opened after many difficulties," South Korea's main envoy Chun Yung-woo said, referring to the long break, the North's nuclear test and UN sanctions.

North Korea's state media kept up its tough rhetoric against Washington, saying US-South Korean military preparations showed "the United States is trying to pull a dirty business against the (North) behind the curtain of talks."

"This is clear proof that it is seeking to vanquish (North Korea) with a military strong arm, whetting its sword of aggression under the mask of dialogue," North Korea's Party newspaper Rodong Sinmun said in a commentary carried by the country's official Korean Central News Agency.

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