BEIJING - North Korea has threatened to test a nuclear weapon unless Washington accepts Pyongyang's conditions for a freeze of its nuclear weapons program, a senior U.S. official said.

North Korea said it wants hefty energy aid in exchange for the freeze, calling on the United States to make a "responsible, bold decision." The demands came at six-nation talks today.

Two previous rounds of disarmament talks have made little progress, and the North Korean threat of a nuclear test suggested the latest round may be unsuccessful, said a senior U.S. official in Washington, speaking on condition of anonymity. The other participants are South Korea, China, Japan and Russia.

Today, the start of a group meeting was delayed while Chinese and North Korean envoys met privately, said a South Korean official who asked not to be identified further.

China canceled a planned closing ceremony Saturday, the Chinese Foreign Ministry said without explanation. Two earlier rounds of six-nation talks in the Chinese capital have ended with closing ceremonies.

The United States has been insisting on complete disarmament by the communist state and submitted a proposal to this week's conference in Beijing outlining a step-by-step plan and the benefits North Korea could receive if it complies.

Today, the North renewed a demand for the United States to drop its "hostile policy," though it made no public response to the American proposal. "It is high time the U.S. made a responsible, bold decision," said the North Korean official newspaper Minju Joson, quoted by the North's main news agency.

North Korea's own proposal reportedly calls for energy aid in exchange for freezing its main nuclear facility at Yongbyon. It was unclear whether that included a commitment to dismantle the program.

"The most concrete ... and specific proposal on the table is that made by the United States yesterday with the support of other governments who were there," State Department spokesman Richard Boucher said in Washington. "We look to the North Koreans to study that proposal seriously."

The North Korean envoy, Vice Foreign Minister Kim Gye Gwan, spoke with U.S. Assistant Secretary of State James Kelly in a 2½-hour private discussion on Thursday.

There was no indication of when North Korea might carry out its reported threat to test. The United States thinks North Korea has at least one or two nuclear weapons, with the potential for several more.

Near the end of their discussion, Kelly told Kim that there was little trust of North Korea in Washington and that Kim's statements wouldn't improve matters, the senior U.S. official said.

Thursday was not the first time a North Korean diplomat issued a nuclear test threat. A similar warning came during a meeting between North Korean diplomat Ri Gun and Kelly 14 months ago, also in Beijing.

Ahead of this week's talks, the United States had been hoping North Korea would be willing to meet disarmament demands in return for a brighter economic future for its impoverished people and broader diplomatic acceptance in the region and beyond.

On Thursday, North Korea demanded massive energy aid in exchange for a nuclear freeze, the Kyodo news agency of Japan reported, citing diplomatic sources.

The report said Pyongyang asked for the equivalent of 2,000 megawatts of power per year - comparable to an estimated one-fourth of its current total consumption.

Both Japan and South Korea say they would consider giving the North fuel oil if it freezes its nuclear program as a step toward its eventual dismantling.

Russia would be willing to help provide energy aid and security guarantees, said Russian envoy Alexander Alexeyev, according to the Russian news agency ITAR-Tass. The report did not say what conditions Russia might attach to that offer.

Kim said earlier that his government was developing nuclear weapons for protection from possible U.S. attack.

"If the United States gives up its hostile policy toward us ... we are prepared to give up in a transparent way all plans related to nuclear weapons," he said.