(CNSNews.com) - U.S. lawmakers on Thursday will hear intelligence reports indicating that North Korea provided Syria with nuclear know-how, a development that could break, or further complicate, deadlocked efforts to shut down Pyongyang's nuclear weapons programs.

How Kim Jong-il reacts to the U.S. move remains to be seen, but the reclusive North Korean leader has a history of sensitivity to even mild criticism, particularly from Washington.

An agreement to denuclearize North Korea in exchange for diplomatic and economic concessions has stalled over its failure to provide a full accounting of its nuclear activities, including proliferation. An Israeli airstrike on a facility in Syria last September prompted speculation that the target was a joint Syrian-North Korean nuclear project.

After months of delays, the Bush administration has agreed that intelligence officers will brief lawmakers on Thursday on North Korea-Syria proliferation. Unnamed officials have told major U.S. media organizations that key congressional committees will hear that Israel hit a nuclear facility inside Syria that was being constructed with North Korean help.

Lawmakers reportedly will be shown satellite photos of a now-destroyed facility in Syria resembling North Korea's own plutonium-based nuclear reactor at Yongbyon, some 60 miles north of Pyongyang.

The House and Senate select intelligence committees both have closed meetings scheduled for Thursday, and the Senate Armed Services Committee also plans to hold a closed meeting "to receive a briefing on a sensitive intelligence matter."

A briefing to reporters apparently will come later.

Defense Secretary Robert Gates said Wednesday that the American public could learn what the government believes on the issue "soon."

In recent weeks, the administration has drawn fire from the right over concerns that, in a bid to break the stalemate and achieve a deal, it may be lowering the bar for North Korean compliance in the denuclearization agreement negotiated at "six-party" talks last year.

Specifically, critics worry that the U.S. during a recent meeting with North Korean officials in Singapore softened demands for a full nuclear declaration, which was supposed to be made by the end of 2007. Instead, the U.S. reportedly agreed to accept North Korea's simple acknowledgement -- in a confidential document -- of U.S. concerns about proliferation and about a uranium-based program Pyongyang has long denied having.

On Thursday morning, a U.S. team headed by the State Department's director of Korean affairs Sung Kim arrived in Seoul after a two-day visit to North Korea aimed at pushing forward the arrangement negotiated in Singapore earlier this month.

The diplomatic concessions promised to North Korea in return for its fulfillment of obligations in the six-party agreement include economic aid, removal from the U.S. government's list of terror-sponsoring states, and an end to U.S. sanctions under the Trading with the Enemy Act.

On Wednesday, California Republican Rep. Ed Royce said at a hearing of a House Foreign Affairs Committee subcommittee on Asia that the U.S. was "moving the goal posts ... in North Korea's favor."

"Success can't be built on compromised principles with an opaque regime that has shown only a desire to extract concessions from the United States," he said.

"An actual declaration from the North Koreans on all aspects of is nuclear programs would have been a signal that the regime is serious about giving up its weapons, not just buying time and trying to extort aid," Royce added.

North Korea has denied allegations of proliferation, and the making public of intelligence proving otherwise will likely have an impact on the denuclearization negotiations -- although exactly what impact is unclear.

Some news reports say the briefings are meant to persuade lawmakers about the importance of pressing ahead with the six-party talks process, while others said they were intended to prod the North Koreans to admit the proliferation.

Still others suggested that the timing of the briefings suggest that administration hawks doubtful about North Korea's trustworthiness are trying to sabotage the State Department's efforts to break the deadlock.

Last October, the non-profit Institute for Science and International Security released commercial satellite images of the suspected site of the Israeli air strike, a location near the Euphrates River, about 90 miles from Syria's border with Iraq.

The images, captured a month before the Sept. 6 strike, showed a large, box-like structure which ISIS analysts said was similar in shape to North Korea's Yongbyon reactor.

On Sept. 11, a North Korean foreign ministry spokesman called the Israeli action "a very dangerous provocation" and voiced "solidarity" with Syria.

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