WASHINGTON (CNN) -- A covert nuclear reactor destroyed last year in Syria would have been capable of producing plutonium and probably was "not intended for peaceful purposes," the White House said Thursday.

Israeli soldiers in the Golan Heights look toward Syria on September 7, 2007, a day after an Israeli airstrike.

But senior intelligence officials later said they had only low confidence that the facility was meant to build nuclear weapons.

A senior U.S. official said the reactor was weeks or months away from being functional when it was bombed by Israel in September.

"This thing was good to go, so we had to assume they were ready to throw the switch," said a senior U.S. intelligence officer who, along with another senior intelligence officer and a senior White House official, briefed reporters about the site Thursday afternoon.

A White House statement said North Korea may have assisted Syria's nuclear activities.

"We have long been seriously concerned about North Korea's nuclear weapons program and its proliferation activities," the statement said. "North Korea's clandestine nuclear cooperation with Syria is a dangerous manifestation of those activities."

At the media briefing, one of the intelligence officials said information collected by the United States suggests North Korean "nuclear entities" met with high-level Syrian officials as early as 1997.

In 2005, the investigators learned that Syria and North Korea were working together on a project in a remote part of the Dayr az Zawr region of eastern Syria, the official said.

A working reactor would make Syria the first Arab nation with nuclear capability and would potentially put nuclear weapons in the hands of a regime that the United States accuses of committing human rights abuses and supporting international terror groups.

During the briefing, the intelligence officials said they had "high confidence" that North Korea had aided Syria with its nuclear program. But they said they have only low confidence about concluding that it was meant for developing weapons. That's in part because the site had no reprocessing facility, needed for making bombs.

The nation's most senior intelligence officials spent much of Thursday briefing key lawmakers on the September bombing by Israeli warplanes.

The officials showed a narrated video with still photographs and animated images they said indicate similarities between the Syrian facility and North Korean nuclear facilities. Watch the video that U.S. officials say shows the nuclear reactor »

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"The reactor would have been capable of producing plutonium for nuclear weapons, was not configured to produce electricity and was ill-suited for research," CIA Director Michael Hayden said in a message, obtained by CNN, that he sent to employees Thursday.

In the message, Hayden said intelligence officers learned last spring that the building was a nuclear reactor built using North Korean technology. He said the CIA had suspected that the countries were cooperating on nuclear technology as early as 2001.

Outside nuclear experts -- none of whom had immediately reviewed the administration video Thursday -- have said that none of the fuel needed to run a nuclear reactor was present on the site.

Asked why David Albright, a former weapons inspector, and other experts have said Syria was not close to getting the reactor functional, a U.S. official said that such comments are coming from people who are "only half-read-in on" the intelligence.

Syria's ambassador to the United States criticized the Bush administration claims, saying Syria never worked with North Korea on a nuclear program. "I hope the truth will be revealed to everyone," Imad Moustapha told CNN's Wolf Blitzer.

"This will be a major embarrassment to the U.S. administration for the second time; they lied about the Iraqi [weapons of mass destruction], and they are trying to do it again."

Pyongyang has resisted pressure to reveal who has received North Korean nuclear know-how.

On Capitol Hill, the briefings raised questions about how the news would affect ongoing six-party talks in which the United States and other world powers are trying to get North Korea to give up its nuclear program in return for the loosening of sanctions.

Rep. Pete Hoekstra, the top Republican on the House Intelligence Committee, said the briefing had come eight months too late.

And he warned that the briefing would complicate the talks with North Korea, saying it "would be much harder to go through Congress and get [any] agreements approved." Watch Hoekstra lash out »

Rep. Howard Berman, the Democratic chairman of the House Foreign Affairs Committee, issued a statement calling the reported details about the site "disturbing." But he said they provide no reason to suspend talks with North Korea.

"Rather, the information that has been released to the public demonstrates the importance of insisting on a verifiable enforcement mechanism to ensure that North Korea honors its commitments to stop spreading the means to create nuclear weapons and to end its nuclear program permanently," he said.

Officials said they delayed releasing details of the September 6 Israeli air strike for fear that doing so would provoke Syria to retaliate against Israel, leading to major warfare in the region.

In their briefing with reporters, the senior officials said that Israel had consulted the United States before launching the strike that took out the facility but stressed that U.S. officials did not "green light" the action. E-mail to a friend

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