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North Korea was helping Syria build a nuclear reactor, US officials are to tell lawmakers in a closed session.
Unnamed officials told a number of US newspapers that the US had video footage of the Syrian facility with North Koreans inside.
Syria has repeated denials that it has any nuclear weapons programme, or any such agreement with North Korea.
It follows an unexplained air strike by Israel last September on a target inside Syria.
According to the Washington Post, the alleged nuclear facility was the target of the bombing.
'Not operational'
The video footage - said to have been obtained by Israel - also showed striking similarities between the Syrian facility and the North Korean reactor at Yongbyon, reports said.
There was no Syria-North Korea co-operation whatsoever in Syria
Bashar Jaafari
Syrian ambassador to UN

However, the facility was not yet operational and there was no fuel for the reactor, officials said.
The White House has not commented on the reports, but Defense Secretary Robert Gates said information on the issue could be made public "soon".
Syria's ambassador to the UN, Bashar Jaafari, denied the links.
"There was no Syria-North Korea co-operation whatsoever in Syria. We deny these rumours," he said.
North Korea has previously denied transferring nuclear technology to Syria.
In a landmark deal reached in February last year, Pyongyang agreed to close its main reactor and divulge the full extent of its nuclear programme by December.
However, it missed the deadline, and while it is taking steps to close its Yongbyon reactor, it has yet to produce a declaration of nuclear activities to the international community's satisfaction