FACTBOX: U.N. watchdog launches nuclear probe in Syria

(Reuters) - The International Atomic Energy Agency will investigate U.S. intelligence allegations made this week that Syria built an atomic reactor with North Korean help before it was destroyed in an Israeli air strike last year.

Following is an outline of the IAEA and Syrian approach to the issue, which Washington said could have posed another nuclear proliferation peril in the Middle East on top of Iran's secretive uranium enrichment program.

Israel is widely believed to have the Middle East's only nuclear arsenal which experts say has as many as 200 warheads.

* UN WATCHDOG IN THE DARK UNTIL THIS WEEK

After a September 6 Israeli bombing raid that destroyed an unspecified target in Syria, nuclear analysts cited satellite imagery they said indicated it was a nuclear reactor of North Korean design. The United States and Israel refused comment while Syria denied hiding anything from IAEA inspectors.

The IAEA launched an inquiry and nudged Syria, in the interest of transparency, to allow its inspectors to visit the site. Syria refused, which stymied the investigation.

But IAEA Director Mohamed ElBaradei said the agency's search for truth was also hamstrung by a failure of others, an allusion to the United States and Israel, to pass on "a shred" of relevant evidence despite requests for it. He accused Israel of a "bomb first and ask questions later" approach that set back the cause of IAEA sleuthing for proliferation threats globally.

After months of silence, Washington passed information on the alleged reactor to the IAEA this week while briefing members of Congress and reporters.

* SYRIAN REACTION

The Syrian government said Israel's target was a disused military building without any nuclear connection and that it was hiding nothing from the U.N. atomic watchdog.

Satellite imagery taken after the air strike and cited by Western analysts showed it had been razed with a new building erected on it. They said Syria's swiftness to remove whatever had been there suggested it had something illicit to hide.

After Washington's disclosure of some of the intelligence on Thursday, Syria compared the allegations to those made against Iraq about weapons of mass destruction that were never found.

* THE IAEA'S NEXT STEPS

ElBaradei said the IAEA would treat the allegations "with the seriousness they deserve". The agency may renew calls on Damascus to let inspectors examine the location and may seek to interview knowledgeable Syrian officials.

* CRITICAL GAPS IN THE INTELLIGENCE

The findings aired by the Central Intelligence Agency contained no evidence that Syria had any uranium fuel to power the reactor or a reprocessing plant needed to convert spent fuel into weapons-grade plutonium.