VIENNA, Austria — An initial probe of American allegations that a Syrian site hit by Israeli warplanes was a secretly built nuclear reactor is inconclusive and further checks are necessary, a senior U.N. atomic inspector said today.

A deputy director general of the International Atomic Energy Agency, Olli Heinonen, said he was satisfied with what was achieved on his four-day trip but “there is still work that needs to be done” in following up on the claims that Syria was hiding elements of a potential nuclear arms program.

A senior Syrian official saw it differently, however. Vice President Farouk al-Sharaa told the Hezbollah-owned Al Manar TV station that his country allowed the inspectors to visit the site in the remote eastern desert to prove the accusations from Washington are false.

Mr. Heinonen spoke to reporters after arriving on a flight from Damascus back to Vienna, headquarters of the IAEA. He met in the Syrian capital with officials in charge of the nation’s nuclear program and senior Syrian generals. Damascus claims that the building flattened by Israel was a non-nuclear military structure.

With Syrian authorities imposing a virtual news blackout on his trip, few details had surfaced beyond the fact that Syrian authorities allowed the three-man inspecting team to visit the Al Kibar site targeted in September. Al-Sharaa’s comments were the first from Syria on the IAEA probe.

Washington hopes that the U.N. agency team is carrying persuasive evidence backing American intelligence that the structure hit by Israel in September was a nearly completed plutonium-producing reactor.

If so, the trip could mark the start of an investigation similar to the probe Iran has been subjected to over the past five years. The process could draw in countries like North Korea, which Washington says helped Damascus, and Iran, also linked by media reports to Syria’s nuclear strivings.

But Mr. Heinonen declined to tip his cards on what he and his team had been able to see and do beyond acknowledging they were able to take environmental samples in the large area where material from the site may have been spread by the exploding Israeli ordnance.

“We achieved what we wanted on this first trip,” he said. “We continue our discussions, we took the samples we need to take and now it’s time to analyze them and also look at the information we got from Syria.

“We will see in the days and weeks what will happen next,” he said when asked about the chances of another visit.

Syria agreed to allow the nuclear inspectors to visit the bombed Al Kibar site in early June only after months of delay. And even before the IAEA team left for Damascus on Saturday, Syrian authorities had already said three other locations suspected of possibly harboring secret nuclear activities were off limits.

IAEA officials had sought to play down heightened expectations ahead of the trip. The agency has little formal inspection rights at Syria, which has only a rudimentary declared nuclear program revolving around research and the production of isotopes for medical and agricultural uses, using a small, 27-kilowatt reactor.

Ahead of the trip, a Vienna-based senior diplomat briefed on the inspection team’s agenda said they would ask for information related to allegations of secret Syrian nuclear procurements, either from North Korea or the nuclear black market headed by a Pakistani scientist, A.Q. Khan.

A traditional method at suspected nuclear sites — taking swipes in the search for radioactive traces — should be of no use at Al Kibar. That’s because none had been introduced into the alleged reactor before it was struck by Israel, according to intelligence given the agency, both by America and Israel and subsequently by other sources.

So the inspectors focused on other telltale signs — minute quantities of graphite, for instance, which is used as a cooling element in the type of North Korean prototype allegedly being built with help from Pyongyang. Such a reactor contains hundreds of tons of graphite, and any major explosion would have sent dust over the immediate area.

But — if the Syrians are interested in a cover-up — they could have scoured the region to bury, wash away and otherwise remove any such traces.

And although American intelligence says the reactor was close to completion, it is possible any graphite elements were not yet installed at the time of the Sept. 6 bombing.

The inspectors also were expected to have looked for traces of other metals and substances commonly contained in the type of reactor that the Syrians were suspected of building.