Commercial satellite images show construction in eastern Syria that resembles the early stages of a small, North Korean-model nuclear reactor, independent experts said in a report Wednesday, speculating that it was the site hit last month in an Israeli airstrike.

The photos, taken nearly a month before the Sept. 6 strike, show a tall, box-like building near the Euphrates River that the report said was similar in shape to a North Korean 5-megawatt reactor building in Yongbyon.

It cautioned that the Syrian building was "not far enough along in its construction to make a definitive comparison." The photo also shows a smaller building on the river that the report says appears to be a pump station, which would be needed to provide water to cool a reactor.

The report was authored by David Albright, a former U.N. nuclear inspector and now head of the Washington-based Institute for Science and International Security, and ISI researcher Paul Brannan.

The Israeli airstrike has been shrouded in mystery. Israel has been extremely secretive about the affair, only recently relaxing censorship to allow Israel-based journalists to report that its aircraft attacked a military target deep inside Syria on Sept. 6.

Earlier this month, the New York Times reported that the strike had targeted a partially built nuclear reactor, made with North Korean help, that was years away from completion, citing U.S. and foreign officials.

Syria has repeatedly denied it was building a nuclear facility, and President Bashar Assad has said Israel bombed an "unused military building" in the raid. On Wednesday, a Foreign Ministry official denied earlier media reports that satellite photos showed what could be a nuclear reactor.

"Syria strongly denies the reports that the targeted site is a nuclear facility," the official told AP, speaking on condition of anonymity because of the sensitivity of the subject. The official described the reports as "part of a continuing campaign of accusations against Syria."

The ISIS report offered no evidence the site shown in the photos was the one hit by Israel. The photo, taken by the private satellite imagery firm DigitalGlobe, was taken on Aug. 10, and the report did not say if images of the site after the strike were available.

The authors of the report did not immediately return calls seeking comment.

An image published in the report shows a tall, square building in the desert about 750 yards from the river, near the town of Deir al-Zour, 250 miles northeast of Damascus.

If the building does contain a reactor similar to the Yongbyon site, it would likely be a 20-25 megawatt gas-graphite reactor, large enough to make about one nuclear weapon's worth of plutonium each year, the report said. To build nuclear weapons from such a reactor, Syria would need a separate facility to extract plutonium from the spent fuel from the reactor, it said.

The box-shaped building has a roof, making it impossible to see what is inside. The building is 47 yards square, similar in size to the 48-by-50 yard Yongbyon reactor, the report said.

Along with the possible pump station on the Euphrates River, a secondary structure is visible near the main building, which the report said could not be identified. Several trucks are also visible, along with heavy machinery tracks around the site, which "indicated recent construction activity," the report said. A wider satellite photo shows an airstrip 2 miles to the north.

The report said the images left many questions unanswered — including how much of the construction was completed and whether Syria had obtained any reactor components.

United Nations diplomats last week told The Associated Press that experts from the U.N. nuclear watchdog, the International Atomic Energy Agency, have begun analyzing satellite imagery of the Syrian site.

Diplomats familiar with the issue said initial perusal had found no evidence that the target hit was a nuclear installation. They emphasized that it was too early to draw definite conclusions.

Syria has not declared a nuclear program to the IAEA beyond a small, Chinese reactor it uses for research, which it allows the agency to inspect. North Korea has said it was not involved in any nuclear program in the Mideast nation.