WASHINGTON -- The United States Friday expressed satisfaction that China had joined in voicing concerns over North Korea's uranium enrichment program, which could provide an alternative to plutonium for making nuclear bombs.

"We were pleased ... that the Chinese acknowledging for the first time in the statements that we put out the enrichment program that the North Koreans had and the steps that needed to be taken to deal with it," White House spokesman Robert Gibbs said.

Gibbs was asked to confirm reports that U.S. President Barack Obama told Chinese President Hu Jintao this week that Washington will have to beef up its military presence in Northeast Asia unless Beijing steps up pressure on Pyongyang for its nuclear and missile programs and other provocations.

In a joint statement after a summit here Wednesday, Obama and Hu "expressed concern" over North Korea's "claimed uranium enrichment program."

China, North Korea's staunchest communist ally, had been reluctant to acknowledge the existence of a uranium program in North Korea, citing a lack of first-hand information, although North Korea showed a U.S. nuclear scientist an enrichment plant in November.

The plant could serve as a second way of building nuclear bombs in addition to its existing plutonium program, but Pyongyang insists the facility is producing fuel for power generation.

Gibbs said that the Obama administration has been working closely with China to rein in North Korea's weapons of mass destruction programs and other provocations.

"We have, through the president, through the secretary of defense, through the secretary of state, have worked to express our concern about the aggressive activities of North Korea and to work to bring the Chinese effectively into helping us deal with some of those problems," he said.

Obama and Hu Wednesday also urged North Korea to "avoid further provocations," saying that "the paramount goal must be complete denuclearization of the peninsula."

The leaders also "emphasized the importance of an improvement in North-South relations and agreed that sincere and constructive inter-Korean dialogue is an essential step."

North Korea Thursday proposed that the two Koreas hold a meeting of working-level officials to prepare for a meeting of defense ministers to discuss the artillery attack on South Korea's Yeonpyeong Island and the sinking of the South Korean warship Cheonan, which killed 50 people, including two civilians, last year.

The attacks are issues Seoul wants Pyongyang to address before a resumption of an inter-Korean dialogue or the reopening of six-party talks on the North's denuclearization.

South Korean officials have said they are willing to meet with North Korean officials in mid-February, adding they will also propose a separate meeting to gauge North Korea's sincerity regarding denuclearization ahead of the restart of the six-party talks, which last met in December 2008.

Gibbs welcomed the recent developments, saying, "We're pleased that the South Koreans and the North Koreans are beginning talks."

The euphoria after the summit, however, may be short-lived, critics say.

Bruce Klingner, senior fellow at the Heritage Foundation, said that the joint statement is vaguely worded, calling only for "the necessary steps that would allow for early resumption of the six-party talks."

"Beijing will claim that Washington agreed to return to the nuclear negotiations in the near term, most likely by abandoning its preconditions," the scholar said. "Washington, on the other hand, will underscore that the necessary steps refer to Pyongyang fulfilling Washington's preconditions before six-party talks can be reconvened."

China wants an early resumption of six-party talks without any conditions attached. (Yonhap News)