The US said Syria's reactor was similar to a North Korean one
President George W Bush has defended the recent disclosure of intelligence by the US on suspected nuclear links between North Korea and Syria.
The move was meant as a "message" to the two states and also Iran, he said.
Last week, the White House briefed Congress on what it said was evidence that Syria had been building a secret nuclear reactor with North Korean help.
It presented intelligence seven months after Israel bombed the site. Syria said the US claim was "ridiculous".
The International Atomic Energy Agency (IAEA) has criticised the US for withholding its intelligence.
'Message to Iran'
"We... wanted to advance certain policy objectives through the disclosure," President Bush said at a news conference in Washington.
"One would be to the North Koreans to make it abundantly clear that we may know more about you than you think.
"Then we have an interest in sending a message to Iran and the world, for that matter, about just how destabilising nuclear proliferation would be in the Middle East," Mr Bush said.
He added that the information had been withheld at first amid concerns about the risk of "confrontation" or "retaliation", without elaborating.
The site of the alleged reactor, said to be like one in North Korea, was bombed by Israel in 2007.
White House officials have said it was within weeks or months of completion.
Syrian officials have said the site that was bombed by Israel on 6 September 2007 was an unused military facility under construction.
Building on the site had stopped some time before the air strike, Damascus said.