WASHINGTON —  Faced with an extended stalemate, the Bush administration has asked China (search) to redouble its efforts to lure North Korea (search) back to negotiations on its nuclear weapons program.

The appeal, disclosed by a State Department official on condition of anonymity, reflects a growing frustration over North Korea's refusal to reopen six-nation talks for nearly a year and rhetoric from Pyongyang that administration officials consider alarming.

Last week, some U.S. officials said spy satellites show possible preparations for North Korea's first-ever nuclear weapons test, including the digging and refilling of a large hole at a suspected test site in northeastern Kilju (search) along with the apparent construction of a reviewing stand being erected some distance away.

China should use all the tools available to it to reopen negotiations, said the U.S. official, without elaboration.

The Bush administration on Monday offered a couple of incentives to North Korea -- direct talks and recognition of its sovereignty -- in a bid to reopen negotiations.

But on Tuesday, North Korea again took a hard line, blaming the United States for the impasse in negotiations while dismissing reports that it was preparing a nuclear test.

"The United States is making noise, saying that our country will have an underground nuclear test in June and it will notify the International Atomic Energy Agency, Japan and other related countries," the North's main state-run Rodong Sinmun daily wrote in a commentary, according to the country's official Korean Central News Agency.

"The United States is not behaving normally and is a country we cannot deal with," the paper said.