The U.S. delegation led by Sung Kim - the top U.S. State Department expert on the Koreas - traveled to Pyongyang on Tuesday to press for a list of nuclear programs that the North had promised to deliver by the end of last year.

If the trip produces major progress, Foreign Minister Yu Myung-hwan said he hoped international nuclear talks would resume in May.

"The North's nuclear declaration has been put off, but the U.S. State Department experts' team has been conducting its final work in Pyongyang," Yu told a ministry meeting, according to his office.

The disarmament talks have been stalled for months after Pyongyang missed a December deadline to provide a declaration of its nuclear weapons programs as it promised to do in return for aid and concessions from the U.S. and four other regional powers.

In Pyongyang, Sung Kim discussed the declaration and verification issues with North Korean officials including the country's chief nuclear envoy Kim Kye Gwan, said Max Kwak, a spokesman at the U.S. Embassy in Seoul.

Sung Kim was expected to meet North Korean nuclear experts Wednesday, Kwak said.

The U.S. delegation was to return Thursday to Seoul and fly back to Washington the next day, he said.

Recently, the U.S. has backed away from its demand for a "complete and correct" declaration that would cover all North Korea's past activities, including allegations of a secret uranium enrichment program and nuclear cooperation with Syria.

Now, U.S. officials say North Korea would simply "acknowledge" the allegations and that controls would be set up to verify it does not engage in such activities in the future.

U.S. lawmakers were to be briefed later this week about intelligence suggesting that North Korea was helping Syria build a reactor similar to the North's main nuclear facility. The site of the alleged reactor was reportedly bombed by Israel last September.