Inspectors led by the International Atomic Energy Agency's number two, Olli Heinonen, are flying out to examine a building which the United States alleges was a covert nuclear reactor built with North Korea's help, until it was destroyed in an Israeli air attack last September.

The trip -- from June 22-24 -- was announced by IAEA chief Mohamed ElBaradei at the regular summer meeting of the watchdog's 35-member board of governors earlier this month after the US passed on intelligence suggesting the building was a covert nuclear reactor close to becoming operational.

Damascus, a US foe and ally of Iran, has dismissed the allegations as "ridiculous" and insists the edifice was a disused military building.

But following the Israeli bombing, Syria appears to have wiped the destroyed site clean of rubble late last year and erected a new building, making any potential investigation by the IAEA more difficult.

Both Syrian President Bashar al-Assad and the country's atomic energy agency chief Ibrahim Othman have pledged Syria's cooperation with the IAEA.

But diplomats in close to the Vienna-based organisation have said Damascus is only allowing inspectors to visit the bombed site Al-Kibar, but not two or three other suspect sites that the watchdog is interested in.

In an interview with Dubai-based Al Arabiya television this week, ElBaradei said there was no evidence Syria had the skilled personnel or the fuel to operate a large-scale nuclear facility.

"We have no evidence that Syria has the human resources that would allow it to carry out a large nuclear programme. We do not see Syria having nuclear fuel," ElBaradei said.

The Egyptian-born diplomat said the IAEA only had pictures of a site in Syria bombed by Israel last year, which resembled a nuclear facility in North Korea.

He reiterated his call on Damascus to cooperate.

Washington is nevertheless adamant that the allegations are true.

"The reality here is that there's some pretty strong evidence out there about what Syria was doing," said State Department deputy spokesman Tom Casey on Tuesday.

"We hope that the Syrian Government has many, many, many more opportunities to explain directly and in detail to the IAEA exactly what they were doing and what their activities were and how they were engaged in nuclear technology."

According to a report in the French daily Le Monde on Thursday, the IAEA also has intelligence from other countries which backs up the US case.

The newspaper, without revealing its sources, said that the information included satellite photos from "different countries", as well as information from the IAEA's own past investigations into North Korea's nuclear activities.

The IAEA declined to comment on the report when contacted by AFP.

US envoy Gregory Schulte pointed out the great lengths to which Syria went to clean up the site and destroy any evidence of what had existed at Al-Kibar.

US intelligence suggested that Syria had conducted a controlled demolition of the building and had removed equipment and debris.

"Much of the work took place at night or under the cover of tarpaulins," Schulte told the IAEA board meeting earlier this month.

"Syria's obfuscation and concealment efforts raise many troubling questions," the US envoy said.

If the reactor was intended for a civil nuclear energy programme, "why go to such lengths to cover up its clandestine activities? What does Syria have to hide?"

Other IAEA board members were also troubled by the allegations.

"We expect the Syrians to provide the IAEA with all the access it requests," an EU diplomat told AFP.

The inspectors' findings are expected to be published in a report to be discussed at the IAEA's next regular board meeting in September.

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