By Jonathan Marcus
Diplomatic correspondent, BBC News
When Israel attacked critics doubted if the target was a nuclear reactor
The US has made explicit allegations that the target hit by Israeli warplanes in Syria last September was a nuclear reactor under construction.
It was being built with help from North Korea, the Bush administration said.
But the White House statement - after a series of intelligence briefings on Capitol Hill - raises many questions.
As does the decision to go public just as international talks to try to roll back North Korea's nuclear weapons programme have hit a critical stage.
The Bush administration is clear - the target of the Israeli air raid last September was an unfinished nuclear reactor being built in Syria with the help of North Korean know-how and technicians.
'More evidence needed'
The intelligence briefings on Capitol Hill apparently included remarkable photos obtained by the Israelis from inside the facility which are said to confirm the North Korean link.
Many experts - not least in the US - were sceptical after the air strike, doubting that the target was actually a nuclear reactor.
And they are going to require more public evidence before they will be convinced.
If this was a clandestine nuclear programme, was it, as the administration contends, intended to develop a plutonium-based bomb?
If so, where are the other facilities that would be needed for such a project; a plutonium separation plant or a centre to actually assemble a weapon?
Where would the uranium fuel for such a reactor have come from?
And just how far advanced was the project when the Israelis struck?
Equally what is not clear is the purpose of Thursday's US briefings and the White House statement.
True it certainly puts additional pressure on the governments of Syria and North Korea - both countries that are high on the table of international public enemies as far as the Bush administration is concerned.
But one key question concerns the impact that these very public US allegations might have on the six-party nuclear talks with North Korea.
These seemingly interminable discussions intended to roll back Pyongyang's nuclear weapons programme have reached a critical juncture.
Reports suggest significant progress is being made, but that the US has agreed not to force North Korea to account for its alleged proliferation activities, notably in Syria.
Is this then an attempt by Washington to clear the air ahead of a subsequent agreement?
Or is it, as some arms control experts fear, a sign that the more hawkish voices within the administration have won the internal battle and are actively trying to scupper what they see as a bad deal with Pyongyang?