VIENNA, Austria, (AP) – Syria has blocked a new visit by International Atomic Energy Agency experts seeking to follow up on intelligence that Damascus built a secret nuclear program built with the help of North Korea, diplomats told The Associated Press on Saturday.

The diplomats also said Washington was circulating a note among members of the IAEA board opposing a Syrian push for a seat on the 35-nation board. The board normally works by consensus and a seat held by Damascus could thus hamper any investigation into its alleged nuclear activities.

Syria fears a massive atomic agency investigation similar to the probe Iran has been subjected to more than five years.

“Syria’s election to the board while under investigation for secretly … building an undeclared nuclear reactor not suited for peaceful purposes would make a mockery” of the Nuclear Nonproliferation Treaty, said the note, as read to the AP.

The diplomats said that the U.S. was pushing to encourage Kazakhstan to challenge Damascus for the seat, but the Kazakhs apparently are reluctant to do so, fearing lack of support.

Syria rejected the IAEA request for a visit late last month, the diplomats said. The visit would have been a follow up to an initial trip by IAEA inspectors in June.

“The Syrians said that a visit at this time was inopportune,” said a senior diplomat, who, like two others agreeing to discuss the issue, demanded anonymity because their information was confidential.

That appeared to leave open the possibility of a later visit. But one of the other diplomats said members of the Syrian mission to the IAEA were spreading the word among other missions that further trips beyond the one in June were unlikely.

If so, that could cripple international efforts to probe U.S. allegations that a site in a remote part of the Syrian desert, which Israel destroyed last year, was a near-finished plutonium-producing reactor built with North Korean help, and that Damascus continues to hide linked facilities.

IAEA experts came back June 25 from a four-day visit, carrying environmental samples from the Al Kibar site hit by Israel in September. Those are now being evaluated.

But the results might fall short of providing a conclusive results.

A traditional method at suspected nuclear sites — taking swipes in the search for radioactive traces — was unlikely to have been of 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 to the agency by the U.S., Israel and a third country the diplomats declined to identify.

So, the inspectors also looked for minute quantities of graphite, which is used as a cooling element in the type of North Korean prototype that was 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 were interested in a cover-up — they would have scoured the region to bury, wash away and otherwise remove any such traces. And although U.S. intelligence says the reactor was close to completion, it is possible that graphite elements were not yet installed at the time of the Sept. 6 bombing.

If so, the initial probe might be inconclusive, making further trips necessary. The agency also is interested in going to three other locations suspected of possibly harboring other secret nuclear activities — sites the Syrians insist are off limits.

More broadly, IAEA experts had hoped to use a follow-up visit to put questions to Syrian officials based on the intelligence available to them outlining years of extensive cooperation between the Syrians and teams of visiting North Korean nuclear officials.

North Korea exploded a nuclear device in 2006. The North is believed by experts to have produced enough weapons-grade plutonium to make as many as 10 nuclear bombs before agreeing to dismantle its weapons program early last year.

But the diplomats said Syria was strenuously denying any concerted North Korean presence in the country — despite U.S. intelligence alleging that the building bombed was reactor of the type only built by the communist state.

They said Syrian officials described meetings between nuclear officials from Pyongyang and their Syrian counterparts occasional and informal, despite intelligence information to the contrary.