Sung Kim, who left Seoul for the communist state's capital on Tuesday for discussions on an international nuclear disarmament deal, was not immediately available for comment after crossing back, a US Embassy official said.

North Korea's official KCNA news agency quoted an unnamed Foreign Ministry spokesman as saying: 'The negotiations proceeded in a sincere and constructive manner and progress was made there.' North Korea failed to meet a Dec. 31, 2007 deadline set in the six-way nuclear deal to give a complete list of its fissile material and nuclear weaponry as well as answer U.S. suspicions of proliferating technology to Syria.

The spokesman said technical matters of the nuclear declaration were discussed but offered no details.

The White House has said little about the possibility of cooperation between North Korea and Syria since Israel conducted a mysterious Sept 6 air strike on Syria that media reports said targeted a nuclear site being built with Pyongyang's help.

The briefing with US lawmakers is on Thursday, a US official said. -- REUTERS