The UN atomic watchdog's probe into alleged illicit nuclear work in Syria has been delayed because the agency's contact man in Syria was murdered, IAEA chief Mohamed ElBaradei revealed Thursday.

"The reason that Syria has been late in providing additional information (is) that our interlocutor has been assassinated in Syria," ElBaradei told a closed-door session of the International Atomic Energy Agency's 35-member board. A recording of his remarks was obtained by AFP.

He did not provide any further details about the identity of the man or circumstances of the assassination.

But according to Arab media reports last month, a brigadier general thought to be the Syrian regime's liaison with Hezbollah in Lebanon was assassinated.

The Saudi-owned pan-Arab daily Al-Hayat said the victim was a senior Syrian officer "in charge of sensitive files and closely linked to the Syrian top brass."

Al-Bawaba, an Arab news website, named the officer as Mohammed Sleiman, saying he was "Syria's liaison officer with Lebanon's Hezbollah movement."

The Lebanese anti-Syrian daily al-Mustaqbal quoted a Syrian news site as saying Sleiman was the head of security at the presidential palace in Damascus and President Bashar al-Assad's "right-hand man."

ElBaradei's revelation came on the fourth and final day of the IAEA board meeting, where Syria was the final matter of debate.

During the discussions, Western countries, and the United States and Australia in particular, complained that Syria was dragging its feet in the IAEA investigation.

Washington claims that Damascus had been building a clandestine nuclear facility at Al-Kibar, a remote desert area of northeastern Syria on the Euphrates River, until it was bombed by Israeli planes in September 2007.

Syria has denied the allegations as "ridiculous," saying the edifice was simply a disused military building.

While Syria allowed a three-member IAEA team to visit the site in June, it has since refused any follow-up trips.

ElBaradei said the IAEA was still evaluating samples taken from the site, but that inspectors had found "no indication" so far of any nuclear material.

He also said that Syria had not yet responded to IAEA requests for additional access to individuals, sites and information.

During the debate, the US envoy to the IAEA, Gregory Schulte, called for "a comprehensive report" by agency inspectors in time for the next board meeting in November.

The report should "detail, in writing, the status of the investigation in Syria and Syria's cooperation with that investigation," Schulte said.

ElBaradei replied that a report would be submitted as soon as possible.

"We have not provided a report and we will provide a report as and when we have enough facts assessment to provide a report," he said.

"Our decision on the report will be based, not on politics, but on when we are ready with assessment and facting (sic)," ElBaradei said.

He insisted that he was not trying to be evasive.

"I'm just telling you how difficult, how complex the situation has become, particularly after the evidence has been eliminated and if we were not to find nuclear material."

Washington claims the facility was being built with North Korean help and resembled Pyongyang's Soviet-type nuclear reactor at Yongbyon used to produce plutonium for nuclear weapons.

US officials allege that Damascus undertook extensive efforts to clean up the site after it was bombed and has since constructed a large building where the reactor stood.

ElBaradei said the cooperation shown by Syria so far was "good" and criticised the Israeli decision to bomb the site.

"I am, as I said last time, quite concerned that with the gratuitous use of force before we have been able to get access to the evidence and once the evidence has been eliminated, it is becoming quite difficult for us to establish the facts," he said.

"We are in a very awkward situation, because the corpse has gone, and we are now at a stage when we have to reconstruct a facility that is not there," he said.