New commercial satellite photos show that a Syrian site believed to have been attacked by Israel last month no longer bears any obvious traces of what some analysts said appeared to have been a partly built nuclear reactor.

Two photos, taken Wednesday from space by rival companies, show the site near the Euphrates River to have been wiped clean since August, when imagery showed a tall square building there measuring about 150 feet on a side.

The striking difference in the satellite photos surprised even some outside experts who were skeptical that Syria might be developing a nuclear program.

“It’s clearly very suspicious,” said Joseph Cirincione, an expert on nuclear proliferation at the Center for American Progress in Washington. “The Syrians were up to something that they clearly didn’t want the world to know about.”