The chief US negotiator to the six-party nuclear talks said on Wednesday night that the US side felt it "worth continuing" the discussion, after the six parties agreed the talks to extend to Friday.

"We feel it is worth continuing this discussions," Assistant US Secretary of State Christopher Hill told reporters at the hotel, adding the US side are "encouraged about the progress and are pleased to stay a couple of days".

He said head of the delegation's meeting was held on Wednesday, at which all the parties agreed to extend for another two days through Friday night.

Formally known as the second phase of the fifth round since 2003, the fresh talks involved China, North Korea, the United States, South Korea, Japan and Russia, with focus on the implementation of the joint statement in September 2005.

Under the joint statement, North Korea agreed to abandon its nuclear program in exchange for economic aid and security guarantees.

Hill confirmed that he had informal meetings with his North Korea's counterpart Wednesday and that the two sides may meet again Thursday.

"We have a couple of bilateral talks, informal meetings with the North Korea. I also talked with Kim Kye Gwan," said Hill.

He said the discussions were "frankly very difficult", as they were discussing actual development on the ground and "there was a lot of give and take, a lot of questions".

"We managed to work through some of the issues, but whether we can start implementing the agreement this weekend...time will tell." Hill said.

(Xinhua News Agency December 21, 2006)