The United States says North Korea has stepped up disablement of a nuclear reactor it had been threatening to reactivate.

State Department spokesman Sean McCormack said on Friday that US officials in North Korea report that Pyongyang has removed more fuel rods from the Yongbyon nuclear reactor. He told reporters that puts them "beyond where they were prior to their reversing the disablement."

He says the North has replaced seals, reinstalled surveillance and replaced equipment it had removed from the reactor.

He says the North has begun "to reverse their reversal" of the reactor.

The progress comes after the North agreed to resume a stalled nuclear disarmament process after the United States removed the country from a terrorism blacklist as an incentive.

"There is still work to be done" at reprocessing and fuel fabrication factories, McCormack said. But he added that he expected nuclear talks among China, Japan, the two Koreas, Russia and the United States to resume "in the coming period of time." He would not discuss specifics because host China has not announced the meeting.

On Tuesday, the North let UN monitors back into the nuclear site. A diplomat in Vienna familiar with the International Atomic Energy Agency's work in the North said the agency's three-member team had resumed monitoring on Tuesday.

North Korea stopped disabling Yongbyon in anger over US demands that Pyongyang accept a plan to verify its accounting of nuclear programs as a condition for removal from the terrorism list. The North was threatening to reactivate Yongbyon before the United States agreed to remove it from the list.

Six-nation nuclear talks took on new urgency after North Korea set off a test nuclear blast in 2006. It then agreed to dismantle its nuclear program in exchange for energy aid and other concessions, though negotiations have since been beset by deadlock and acrimony.