China is calling on all nations involved in the North Korean nuclear disarmament process to fulfill their commitments. The subtle warning from the host of the negotiations follows North Korea's announcement Tuesday that it wants further concessions before it dismantles its nuclear programs.

Analysts say North Korea's renewed insistence on immediately having its negotiating partners pay for a light-water nuclear reactor is an embarrassment for China, which worked hard as the host to secure Monday's agreement on a joint statement of principles.

Chinese Foreign Ministry spokesman Qin Gang said he thinks there is no question that North Korea understood what it was agreeing to when it approved Monday's joint statement.

He said those involved in the talks, including North Korea, "should implement their commitments in a serious manner" so as to realize the peaceful denuclearization of the Korean Peninsula.

In the agreement reached Monday, North Korea joined the others in stating that its ultimate aim is to abandon all of its nuclear programs. The six nations acknowledged North Korea's desire to have a civilian nuclear program for electricity, and agreed to take the issue up at an "appropriate" time.

Washington says an appropriate time will be after North Korea dismantles its nuclear weapons programs.

Observers say the pressure is once again on China, as Pyongyang's closest ally, to convince North Korea to stay on track with the plan for nuclear disarmament. Ralph Cossa is an expert on Korean peninsula security issues who heads the Pacific Forum, a research organization in the U.S. state of Hawaii.

"The timing of this North Korean announcement, before the ink is even dry on the Chinese ceremonies, could very well work against Pyongyang's better interests," he explained, " because the Chinese have just got to be getting fed up with these guys."

China is the main supplier of food and fuel to the impoverished communist nation.

In the past, Beijing has been able to get Pyongyang to make concessions - including returning to the negotiations - by offering economic incentives. Analysts say it remains to be seen how far China is willing to go this time to make the North stick to its commitments.