SYDNEY, Australia — Washington's chief nuclear negotiator on North Korea expressed confidence Tuesday that the communist nation will end its suspected uranium enrichment program by the end of the year.

North Korea shut down its main nuclear reactor in July and pledged recently to disable its main nuclear facilities and declare all its nuclear programs by year's end in return for economic aid and political concessions.

"I think ... we will have good reason to believe that whatever uranium enrichment program they have going, they will not have going by the end of the year," Christopher Hill, an assistant U.S. secretary of state, said in Sydney.

Uranium enrichment, a process needed to prepare materials for atomic weapons, has long been suspected as part of the North's programs. The nuclear agreement was the result of six-party talks on shutting down the North's nuclear programs.

A U.S. team of nuclear experts has been in North Korea since Thursday to map out a disablement plan.

North Korea has agreed to disable its Yongbyon complex, which is believed to have produced enough plutonium for perhaps more than a dozen bombs — including the device North Korea detonated a year ago to prove its long-suspected nuclear capability.

Hill said disablement of the Yongbyon complex was an important step toward future possible peace talks.

"It is a very important moment for us to see whether we can actually disable this thing in a way that allows us to go forward, to have North Korea make the psychological break with this nuclear reactor, and understand that we'll continue until there is denuclearization," Hill said.

In an interview with CNN in June, Hill estimated that North Korea possesses "about 110 pounds" of reprocessed plutonium, which he said the country must give up.

In his address to the Sydney Institute think-tank on Tuesday, Hill said shutting down Yongbyon would prevent that amount from getting bigger.