North Korea's announcement that it plans to carry out a nuclear test is worrying its last remaining ally, China. Chinese officials are urging Pyongyang to exercise "calm and restraint" - but have stopped short so far of publicly warning the North or threatening any type of sanctions.

China's response to the North Korean announcement was typically cautious. A Chinese Foreign Ministry official on Wednesday issued a statement saying Beijing hopes North Korea will keep calm and exercise restraint.

China also warned other nations not to take actions that might escalate tensions.

The measured response reflects the dilemma China faces in dealing with its Communist ally and neighbor. On the one hand, China wants to maintain good relations - and at least some influence over the North's actions. On the other, Beijing wants to prevent North Korean leader Kim Jong Il from triggering a nuclear conflict on China's border.

China has hosted six-nation talks aimed at ending North Korea's nuclear weapons programs, but has generally refrained from criticizing the country. Events, however, have caused Beijing to slowly begin siding with the United States, Japan and others in facing up to the North. In July, Beijing - albeit reluctantly - joined other members of the U.N. Security Council in passing a resolution condemning Pyongyang for carrying out missile tests.

Analysts say North Korea's announcement Tuesday of its intention to test a nuclear device is putting more pressure on China to take a firm stance. Politics Professor Robert Ross, an expert on Sino-North Korean relations at Boston College in the United States, says Kim Jong Il is probably hoping Beijing realizes North Korea cannot undergo too much pressure without collapsing.

"In some respects, North Korea is challenging China to actually cause pain, because China understands that the very tools it could use to perhaps bring North Korea to the negotiating table, to compromise its nuclear weapons program, are the very instruments that might actually bring down the North Korean regime," Ross said.

China is North Korea's chief supplier of food and fuel, and could try to pressure the North by cutting off supplies. This, however, could weaken the regime to the point of collapse. Analysts including Professor Ross say Beijing does not want to see a humanitarian crisis that will send a flood of refugees into northern China, nor does it want political instability on its border.

"North Korea in some respects is counting on China to not want that to happen, and thus to limit the amount of pressure it actually puts on North Korea to compromise," he said.

The United States is hoping for concerted pressure on Pyongyang, however. U.S. Secretary of State Condoleezza Rice, in comments clearly aimed at China and South Korea, said Tuesday a nuclear test would cause some states in the region to "reassess" their relationship with the North.

China has yet to make any concrete statement on how it plans to implement the terms of U.N. sanctions against the North that followed the July missile tests.