US chief negotiator Christopher Hill said in Beijing Tuesday morning that the United States and the Democratic People's Republic of Korea (DPRK) were "not able to bridge any differences" in Monday's one-on-one talks.

It was still very difficult for the United States and the DPRK to reach mutual understanding even though there was "no problem" for the two to talk, Hill told reporters when he left the hotel for bilateral talks with the Chinese delegation.

"A lot of differences" still remained between the DPRK and the other participants of the six-party talks, he added.

On the draft common document, which is currently being discussed by the six parties, Hill said the second draft "clearly" reflected each side's comments and was "better" than the first one.

Hill said he believed a solution would be gradually reached through the discussion of the draft.

He also promised that the United Stats would remain committed to talks and try to find a solution with the joint efforts of the other parties.

Participants in the fourth round of the six-party talks on the Korean Peninsula nuclear issue will hold a plenary session Tuesday morning at Diaoyutai State Guesthouse, according to Hill.

This round of talks that groups China, the Democratic People's Republic of Korea (DPRK), the United States, the Republic of Korea(ROK), Russia and Japan, inched into the eighth day Tuesday, and it is still hard to say when it will close.

A 3.5-hour deputy chief negotiators' session for the talks was held here Monday afternoon, at which no concrete result was achieved, according to the press center with the Chinese delegation.

The Russian delegation on Monday denied major differences in the ongoing negotiation and said the talks did not reach an impasse.

"There were no major differences, nor did the talks come to a standstill," said V. Yermolov, deputy head of the Russian delegation.

However, according to Hill, US assistant secretary of state who heads the American delegation, it was still a "tough task" for all the parties to reach a consensus, and a lot of patience was needed.