Syria has yet to accept a request from the UN nuclear watchdog to visit a site where Washington says Damascus covertly built an atomic reactor, and has demanded more details about the proposed trip, diplomats said.
The head of the UN body, the International Atomic Energy Agency, said on May 7 that he hoped to be able to shed light "in the next few weeks" on whether a Syrian facility, bombed by Israel last year, was an undeclared nuclear reactor.
Syria, an ally of Iran whose secretive nuclear program is under UN sanctions and IAEA investigation, has rejected as fabricated U.S. intelligence pointing to an almost completed graphite reactor erected with North Korean help.
Damascus, whose only declared nuclear facility is an old research reactor under IAEA inspection, has said Israel's target was only a disused military building in its eastern desert that had no nuclear link.
At the start of May, the IAEA wrote to Syria asking to see the targeted area. Syrian atomic energy chief Ibrahim Othman visited Vienna on May 9 for talks with the agency's chief, Mohamed ElBaradei, diplomats familiar with the matter said.
Those talks did not produce any agreement on the timing and nature of a trip by senior inspectors, they added.
One diplomat said on condition of anonymity that the agency had received a letter from Damascus earlier this week asking for more details on the proposed visit. The agency has replied and is now waiting for a further response, the diplomat added.
Syria's UN envoy said in late April that Damascus would cooperate with the IAEA inquiry and had "nothing to hide."
ElBaradei has chided the United States for waiting until last month to share its intelligence. Analysts citing fresh satellite photos said Syria had razed the site in the meantime, possibly to erase evidence and put up a new building.
Diplomats close to the IAEA said it would be harder for inspectors to detect evidence than before the bombing of a site where Washington said secret nuclear activity dated from 2001.
It is highly unlikely inspectors would find major components of a reactor or related equipment, but they will want to test for traces of graphite or uranium alloys and examine the local water supply system, Israeli nuclear analyst Ephraim Asculai said in an emailed statement earlier in May.
Another report this month by independent nuclear experts briefed by U.S. officials said Syria went to great lengths to foil aerial surveillance by building a false roof and walls to alter what are the normal telltale contours of a reactor.
Some analysts have questioned whether the U.S. material amounted to proof of any undeclared nuclear arms program.
Gregory Schulte, the U.S. envoy to the IAEA, reiterated on Wednesday the facility at the site was not a typical power or research reactor.
"Syrian authorities have a lot of explaining to do," Schulte told journalists. "They must allow IAEA inspectors to visit the site and ensure there are no other undeclared activities."