Britain believes that Syria should be reported to the UN Security Council over its alleged illicit nuclear activity, Britain's ambassador to the International Atomic Energy Agency (IAEA) said Wednesday.

In a restricted report circulated to member states last week, the UN watchdog said it was "very likely" that a remote desert site in Syria bombed by Israeli planes in 2007 was indeed a covert nuclear reactor, as alleged by the United States.

British ambassador Simon Smith told reporters the report left no option but for the IAEA to refer Syria to the UN Security Council in New York.

"What the director general (Yukiya Amano) has told us about is a case of Syria's non-compliance with its comprehensive safeguards agreement," he said.

"And we, and quite a number of other countries equally convinced as we are, will be arguing that -- as we are obliged to do by the statutes of the IAEA -- this non-compliance needs to be reported to the UN Security Council," added Smith, who is also Britain's ambassador to Vienna.

Damascus has always insisted that the site, known as Dair Alzour, was a non-nuclear military installation but it has provided no evidence so far to back this up.

Aside from a one-off visit in June 2008, Syria has refused to allow IAEA inspectors access, despite repeated requests for cooperation from Amano.

Diplomats say the tougher language of his latest report -- it was the first time that Amano has publicly made such an assessment since the IAEA started investigating the allegations in 2008 -- reflects the watchdog chief's growing frustration with Syria.

Washington has already drawn up and circulated to fellow IAEA board members a draft resolution which will be voted on at the watchdog's regular summer meeting next week.

According to the draft, a copy of which was obtained by AFP, Syria will be found in so-called "non-compliance" with its international obligations and reported to the UN Security Council in New York.

The last time a member state was reported to the UN Security Council was Iran in September 2005.

The US "believes that board action... is critical for preserving the credibility of the IAEA and the safeguards system in light of Syria's continued stonewalling of the agency's investigation," Washington's Charge d'Affaires in Vienna, Robert Wood, wrote in a letter accompanying the draft resolution.

A number of western diplomats believed there was sufficient support on the 35-member board for the resolution to succeed.

While it would be unrealistic to expect the vote to be carried unanimously, "I'm pretty confident from what we're hearing that we're in good shape for the board to make that decision," one diplomat said, speaking on condition of anonymity.

"We're hopeful," said another western diplomat.

Since Amano's report, Syria has written to the IAEA pledging "full cooperation", in a move some diplomats saw as a bid to avoid referral to the UN Security Council.

But a western diplomat who said they had seen Syria's letter described the pledge as "vague" and "unspecific", particularly with regard to the exact form such cooperation would take or the timeframe.

And unless Syria provided such details, any such promises were unlikely to remove concerns about it really had been building at Dair Alzour, diplomats said.