"It is deeply regrettable that information concerning the installation was not provided to the agency in a timely manner and that force was resorted to unilaterally before the agency was given an opportunity to establish the facts," he said.

US intelligence

The US intelligence reports included photographs purportedly taken inside the reactor showing construction of the shield for the reactor core, as well as control rods and refuelling ports on top of the reactor.

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Officials said that the site and the reactor were similar to the nuclear facility in Yongbyon in North Korea.

They alleged that the North Korean government had provided assistance with construction. Damascus has dismissed the accusations as "ridiculous".

In his opening address to the summer meeting of the IAEA's 35-member board of governors, ElBaradei stressed that Syria had "an obligation" to report the planning and construction of any nuclear facility to the body.

"We are therefore treating this information with the seriousness it deserves," he said.

He did not say if Damascus would allow inspectors to examine the al-Kibar site in the country's remote northeast desert.

'Full disclosure'

ElBaradei also called for "full disclosure" from Iran over its controversial nuclear programme.

Noting that the IAEA had spent the past five years seeking to verify Iran's nuclear ambitions, ElBaradei said time was running out.

He said it was "regrettable that we have not made the progress we had hoped for with respect to one remaining major issue, namely clarification of the cluster of allegations and the secretariat's questions relevant to possible military dimensions to Iran's nuclear programme".

Tehran insists that its uranium enrichment programme is peaceful, but a number of countries have accused it of carrying out studies to develop nuclear weapons.