The head of the world's nuclear monitoring agency is indirectly criticizing the United States for holding back intelligence on Israel's 2007 bombing raid on Syria.

On Thursday, the U.S. claimed the target of the raid was a Syrian nuclear reactor -- one not intended for peaceful purposes.

Mohamed ElBaradei, head of the International Atomic Energy Agency, said his agency has now been briefed on the bombing, which happened Sept. 6, 2007.

"The agency will treat this information with the seriousness it deserves and will investigate the veracity of the information," he said in a statement.

But he deplored the lengthy delay in informing the IAEA about the alleged rogue reactor project.

Syria has rejected the U.S. claim, calling it ridiculous.

A nuclear weapons expert told CTV's Canada AM that there are plenty of reasons to be skeptical.

"I don't believe any of them," John Clearwater said, referring to both U.S. claims and Syrian denials.

"To me, the interesting thing is the video evidence the CIA and White House released, because to me, it's not particularly compelling. And in point of fact, this attack on the building was not a U.S. operation. It was an Israeli operation."

If this really was a reactor, that would make the raid the modern-day equivalent of Israel's 1981 attack on the Osirak nuclear reactor in Iraq, Clearwater said.

Israel publicly trumpeted the Osirak attack. In comparison, "officially, Israel still has not confirmed this (latest attack). It does not exist on their radar," he said.

Before-and-after photos made available by the U.S. "really don't tell you very much," he said.

The U.S. has tried to suggest the photos show a reactor design similar to one built in North Korea 35 years ago, but Clearwater say they also show a design similar to a British one -- and the plans for those are publicly available in the British national archives.

"My question is: Where were these photos taken and in what year?" Clearwater asked.

U.S. officials released photos of a North Korean nuclear expert visiting Syria. "I have a picture of me with the guy who built (an) atomic bomb. It doesn't mean I built an atomic bomb as well," Clearwater said.

It's credible that Syria had some type of research program, but it doesn't have the wherewithal to run a full nuclear reactor program, he said.

Clearwater also found it curious that given the massive search the U.S. conducted for Iraq's alleged weapons of mass destruction around the region, "they somehow missed a nuclear reactor."

He is pleased the IAEA will be examining the issue and asking Syria to explain itself, although Clearwater noted that building a reactor isn't illegal under international law.

However, "hiding it is," he said.

With files from The Associated Press