North Korea's premier on Tuesday began a visit to China amid U.S. urging for Beijing to use its influence to prod the North back into nuclear talks — and American hints of possible sanctions if Pyongyang doesn't cooperate.

Chinese officials say they will discuss the nuclear standoff with Premier Pak Pong Ju (search), but haven't given details. Beijing also apparently plans to use the visit to lobby the North to speed up tentative Chinese-style reforms in its decrepit, centrally planned economy.

Pak spent about 20 minutes touring a Nokia mobile phone factory at an industrial park in southern Beijing, where he signed a guest book offering "wishes of prosperity for the communications industry."

He was expected to meet with President Hu Jintao and other Chinese leaders during his trip, which includes a stop in Shanghai, the country's financial capital.

Chinese Foreign Minister Li Zhaoxing (search) said this month that the North expressed willingness to return to talks. But he didn't say whether leader Kim Jong Il's government had attached any conditions.

U.S. Secretary of State Condoleezza Rice (search), visiting Beijing, suggested Monday that the North might face sanctions.

"To the degree that a nuclear-free Korean peninsula gets more difficult to achieve if the North does not (return to the talks) then of course we'll have to look at other options," Rice said.

Rice said she appealed for China to use its status as the North's main ally and aid donor to draw Pyongyang back to the talks, which also include South Korea, Japan and Russia.

"The very strong emphasis of the conversation was to determine how we could, each in our own way — but particularly China — make very clear to the North Koreans that the time has come for them to return to the talks," Rice said.

Beijing insists it has little influence over Kim's isolated Stalinist regime and has resisted U.S. appeals to pressure its ally. China is believed to supply the North with up to one-third of its food and one-quarter of its energy.

Analysts say the North's declaration last month that it has nuclear weapons might prompt China to force Pyongyang back into talks. But they say Beijing might be holding out for a U.S. overture to make the North return willingly.

U.S. and Chinese diplomats met last week in Shanghai with their counterparts from Japan and South Korea to discuss possible steps to get North Korea back to the bargaining table.

The North wants aid and a peace treaty with the United States in exchange for a settlement. The vice president of its parliament, visiting South Africa last week, said it was up to Washington to create unspecified "appropriate conditions" to restart talks.

China has organized three rounds of six-nation talks since the dispute flared in late 2002. Washington said Pyongyang admitted operating a secret nuclear program in violation of a 1994 agreement that gave it oil and other aid for abandoning nuclear work.

On Monday, the North announced that it had increased its nuclear arsenal to counter U.S.-South Korean military threats.

"We have taken a serious measure by increasing (the) nuclear arms arsenal in preparation for any invasion by enemies," said the North's Korean Central Broadcasting Station, according to South Korea's Yonhap news agency.

The broadcast said joint U.S.-South Korean military exercises under way now were "preparation for war against us."

Chinese officials have suggested direct talks between Washington and Pyongyang to break the impasse — an option that the United States has rejected.

"It is not a U.S.-North Korean issue," Rice said. "We are determined that this will be done in a multilateral context."