Israel destroyed the reactor in a September 6 air strike that was initially shrouded in secrecy out of what U.S. officials said was fear that public discussion could prompt Syria, which has long supported militant Palestinian groups, to retaliate.

"We are convinced, based on a variety of information, that North Korea assisted Syria's covert nuclear activities both before and after the reactor was destroyed," said a U.S. intelligence document released to reporters.

The document said the administration had concluded that the suspected reactor would have been able to produce plutonium for nuclear bombs and was "nearing operational capability in August 2007" -- the month before the Israeli strike.

The United States did not give Israel any "green light" to strike the suspected nuclear reactor, a U.S. official said.

Syrian Ambassador Imad Moustapha denied the U.S. charge. "This is a fantasy," he told CNN after being briefed by the U.S. State Department on the U.S. intelligence.

"I hope the truth will be revealed to everybody," he said. "This will be a major embarrassment to the U.S. administration for a second time -- they lied about Iraqi WMDs (weapons of mass destruction) and they think they can do it again."

Washington's main justification for the 2003 U.S.-led invasion was that Iraq had stockpiles of WMDs. Such weapons have not been found.

NORTH KOREAN, SYRIAN IN PHOTOGRAPH?

The roll-out of the intelligence on Syria was in some ways reminiscent of the choreographed presentation of U.S. prewar suspicions on Iraq. It included a half dozen closed-door briefings to members of Congress, a White House statement, and then a presentation to reporters.

In the briefings to lawmakers and reporters, U.S. officials produced before-and-after aerial photographs of the suspected reactor in eastern Syria as well as detailed interior images that they said showed key parts of its components.

One photograph showed what a U.S. intelligence official described as a senior North Korean nuclear expert standing beside a key Syrian atomic official inside Syria.

Senior U.S. intelligence officials said the suspected reactor closely resembled the Yongbyon nuclear facility in North Korea, which tested a nuclear device in October 2006.

The U.S. charges come several months after North Korea missed a December 31 deadline to make a declaration of its nuclear programs in a deal over its nuclear ambitions with the United States, Russia, China, Japan, and South Korea.

Under the deal North Korea promised to disclose all of its nuclear programs and, ultimately, to abandon them and any nuclear weapons it may have.

"We hope that the fact that we have had such detailed understanding of this activity ... will convince them that there is no point in trying to cover up not only proliferation activity but (uranium) enrichment activity and plutonium activity," a senior U.S. official told reporters.

The United States hopes airing its suspicions about Syria will garner more international support to isolate Iran, which Washington accuses of seeking to develop nuclear weapons. Iran says its nuclear program is designed to produce electricity.

"One of our concerns is, is there (an Iranian) connection with North Korea? If there is, we don't know it," said a senior U.S intelligence official. "But is there something going on there that resembles this program that we are talking about in Syria - in Iran. That's a very large concern of ours."

Another official said Washington hopes the disclosures will persuade other nations "to join us in pressuring Syria to change its policies" toward Iraq, Lebanon and Palestinian groups that have launched attacks on Israel.

The United States accuses Syria of allowing insurgents to cross its borders into Iraq and of continuing to interfere in Lebanon despite the end of its military occupation.

It was not clear what effect the disclosures would have on North Korea, which was told about the presentations in advance. Nor was it clear whether they would ease concerns in Congress that the United States may have struck a bad bargain with North Korea.

U.S. President George W. Bush has lost the support of some fellow Republicans on the North Korea deal, but the Democrats who control Congress by and large appear to be more supportive of the path he is following.

Rep. Peter Hoekstra, the top Republican on the House of Representatives Intelligence Committee, said after a briefing on the issue that the administration had lost the trust of many lawmakers.

"This administration has no credibility on North Korea," he told Reuters. "A lot of us are beginning to become concerned that the administration is moving away from getting a solid policy solution to 'let's make a deal' -- regardless of how bad it may be."