Syria has razed a suspected nuclear reactor building that was bombed by Israeli aircraft, according to nuclear experts.
Using commercial satellite images, the Institute for Science and International Security said there were signs of a hasty clean-up of the site that was attacked last month.
"Dismantling and removing the building at such a rapid pace dramatically complicates any inspection of the facilities and suggests that Syria may be trying to hide what was there," ISIS said on its website.
According to the institute, tractors or bulldozers can be seen in satellite images taken on October 24 of where the suspected reactor building had stood, and marks can be seen around the razed part of the site.
ISIS said Iraq followed a similar clean-up strategy in 1991, after the first Gulf war, though the International Atomic Energy Agency (IAEA) and UN inspectors eventually pieced together a full picture of Iraq's activities.
There also appears to be a trench that is more clearly visible than in images taken in August.
This could be the result of the Syrians digging up buried pipelines running from what is possibly the pump station, the only structure still visible, about 800 metres from the main site. The pump station would provide the water for cooling a reactor.
The box-like building was located in Syria's eastern desert, near the village of At Tibnah, about 90 miles from the Iraqi border and a few hundred metres from the Euphrates river.
Some US officials and nuclear experts said the building closely resembled structures associated with a North Korean reactor capable of producing enough nuclear material for one bomb a year. North Korea has denied supplying nuclear material to Syria.
Syria is a member of the non-proliferation treaty (NPT) and maintains what are known as full-scope IAEA safeguards.
It signed the NPT in July 1968 when the treaty opened for signature, and ratified it two months later on September 24. It concluded a safeguards agreement with the IAEA on May 18 1992 which "safeguards" a single small nuclear research reactor in Damascus.
The ISIS images raise the question of whether Syria may be in violation of its agreements with the IAEA. Non-proliferation experts say its behaviour is suspicious but the evidence is not conclusive.
"The Syrians were up to something that they clearly didn't want the world to know about," Joseph Cirincione, an expert on nuclear proliferation at the Centre for American Progress, which is based in Washington, told the New York Times.
Mr Cirincione said the photographic evidence "tilts toward a nuclear programme" but does not prove Syria was building a reactor. He said if Syria was developing a nuclear programme, it would be years away from being operational and thus not an imminent threat.