A Syrian nuclear reactor built with help from North Korea was weeks away from functioning, a top U.S. official said Thursday after lawmakers were briefed on the site destroyed last year by Israeli jets.

The official, who wanted anonymity, told The Associated Press that the facility was mostly completed but still needed significant testing before it could be declared operational.

Still, Syria's ambassador to the United Kingdom denied that North Korea's cooperation with Syria had any nefarious purpose.

"This has nothing to do with North Korea and Syria. They just want to exert more pressure on North Korea. This is why they are coming up with this story," Sami al-Khiyami told Reuters.

"The cooperation between North Korea and Syria has nothing to do with (building) a nuclear facility. Cooperation is mainly economic. ... This is political manipulation ahead of the talks with North Korea to exert more pressure on them," he said.

U.S. lawmakers on Thursday said the construction of a nuclear facility in Syria was a major setback to non-proliferation efforts, even as many questioned the timing of the release of the information.

The reactor was destroyed by Israeli jets in September 2007. Nonetheless, its construction indicates a real threat of the spread of nuclear weapons technology, lawmakers said.

It "is a serious proliferation issue, both for the Middle East and the countries that may be involved in Asia," said Michigan Rep. Pete Hoekstra, the ranking Republican on the House Intelligence Committee.

Intelligence officials told several House and Senate committees that the destroyed site was designed to produce a small amount of plutonium, a highly radioactive substance.

Plutonium-producing reactors are of international interest because the material can be used to make high-yield nuclear weapons or "dirty bombs" that disperse radioactive material when they explode, rendering an area potentially unsafe for humans for years.

The reactor was not finished when it was blown up, but U.S. intelligence officials had acquired videotape and other evidence to demonstrate that it resembled the nuclear reactor at Yonbyon, North Korea. No uranium — the fuel for a reactor — was evident on site.

Syria has maintained that the site was an unused military facility. However, its failure to declare the site to the International Atomic Energy Agency could be a breach of an international nuclear nonproliferation treaty. U.S. officials were also briefing the IAEA on Thursday.

White House press secretary Dana Perino said the Bush administration would issue a public statement later in the day.

Israeli warplanes bombed the Syrian plant on Sept. 6, 2007. Private analysts said at the time it appeared to have been the site of a reactor, based on commercial satellite imagery taken after the raid. Syria later razed the site. A new, larger building has been constructed in its place.

Commercial satellite imagery from January analyzed by the Institute for Science and International Security in Washington shows the new building is 60 meters by 60 meters, compared to the original 47-by-47 building that was destroyed last year. It has a vaulted roof, different from the original flat roof. It appears to be connected by a series of trenches and pipes to a possible water treatment facility.

U.S. officials said Israel shared intelligence with the United States before the bombing after administration officials expressed doubts that the site was a nuclear reactor built with North Korea's assistance, according to The Washington Post, which first reported the existence of the videotape on its Web site Wednesday.

Lawmakers want to know why the Bush administration is releasing details of the reactor now. Sen. Susan Collins, R-Maine, a member of the Senate Armed Services Committee that was briefed by CIA Director Michael Hayden, said she was concerned that the release could expose intelligence-gathering sources and methods.

"I asked repeatedly about that. I'm very concerned. ... What does Syria do now? They can no longer pretend that nothing happened. What does Israel think about this release?" she asked.

"I could think of no good policy reason for releasing this now," she added.

Rep. Gary Ackerman, D-N.Y., chairman of the House Foreign Affairs Middle East subcommittee, accused the Bush administration of selectively leaking the classified information, which he called "bizarre behavior."

While reporters without security clearances were selectively given information, "most of us got no information whatsoever," Ackerman said as he opened a separate hearing on U.S. policy toward Syria.

Ackerman said members of Congress who attend the intelligence briefings later Thursday would be bound to secrecy, and as a result he said many members would stay away from the sessions.

"This is the selective control of information that led us to war in Iraq," Ackerman said.

Hoekstra, too, wondered why the Israeli mission was kept so secretive in September after it happened, but its purpose was being revealed to the press and public in April, before lawmakers were even briefed.

"I think many people believe that we were used today by the administration because — not because they felt they had to inform Congress because it was their legal obligation to do that, but because they had other agendas in mind," he said.

The revelation of alleged North Korean cooperation with Syria comes at a sensitive time for Pyongyang.

U.S. diplomats are pressing North Korea to come clean about its nuclear cooperation with Syria as part of those talks, but they have had little success.

Under an agreement reached last year with the United States, China, Japan, South Korea and Russia, the North is required to give a full account of its nuclear programs, including whether it has spread nuclear technology.

North Korea says it gave the nuclear declaration to the U.S. in November, but U.S. officials say the North never produced a "complete and correct" declaration.

The Capitol Hill briefings come as a U.S. delegation has gone to North Korea to press the regime for a detailed list of its nuclear programs, the latest sticking point at international nuclear disarmament talks.

The Associated Press contributed to this report.