Beijing ? The top U.S. nuclear envoy insisted Friday that North Korea act on its promises to begin nuclear disarmament, hours before a deadline the communist nation was expected to miss to shut down its main reactor.

Assistant Secretary of State Christopher Hill did not say what the consequences would be if the North missed today’s deadline to begin shutting down its sole operating nuclear reactor at Yongbyon as part of a landmark agreement with the U.S. and regional powers.

So far, the North has refused to take action because of a dispute over the release of North Korean funds frozen in a Macau bank.

“There is no reason why the DPRK can’t get on with the task of denuclearization,” said Hill, using the official name of the Democratic People’s Republic of Korea.

“We are not indifferent to missing a deadline. Obviously it is a very important date,” he said. “We will work with our other partners on the appropriate response to the current circumstances,” Hill said in Beijing, where he will meet his Chinese counterpart Wu Dawei today.

As part of the disarmament agreement, the North was supposed to gain access to $25 million in frozen funds at the Banco Delta Asia bank in the Chinese territory of Macau. The bank was blacklisted by Washington in September 2005 for allegedly helping the North launder money and pass counterfeit $100 bills.

The funds were unblocked this week, but North Korea’s Foreign Ministry said Friday it was still confirming the release. The ministry said the country would carry out its side of the February agreement “when the lifting of the sanction is proved to be a reality.”

North Korea alarmed the world in October when it conducted its first-ever underground nuclear test. After a 13-month boycott of nuclear talks, it agreed in February with the United States, China, South Korea, Japan and Russia to give up its nuclear programs in exchange for energy aid and political concessions, along with a U.S. promise to resolve the bank issue.

But Hill said the United States considered the problem resolved.

“It’s certainly worrisome to all of us to see them approaching this date rather lethargically,” he said.

U.S. officials and experts say the process of shutting down a reactor and having U.N. nuclear inspectors verify it would take at least several days – making it virtually impossible for the North to meet today’s deadline.