The United States has released photographs of what it said was a Syrian nuclear reactor built with North Korean help

It is part of an effort to pressure Pyongyang to fully disclose its nuclear activities.

Israel destroyed the reactor in an air strike last September that was initially shrouded in secrecy out of what US 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 US 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 US official said.

Syrian Ambassador Imad Moustapha denied the charge. "This is a fantasy," he said after being briefed by the US State Department on the intelligence.

"I hope the truth will be revealed to everybody," he said. "This will be a major embarrassment to the US 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 US-led invasion was that Iraq had stockpiles of WMDs. Such weapons have not been found.

US 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 US intelligence official described as a senior North Korean nuclear expert standing beside a key Syrian atomic official inside Syria.

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

The US 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.

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