Iran is in the final stages of sanitizing a military site it is suspected of using for secret nuclear weapons-related experiments, two senior diplomats said Tuesday, as the U.N. atomic agency intensified efforts to gain access to the area before the alleged clean-up succeeds in erasing any traces of such work.

Iran, which insists its nuclear program is peaceful contrary to Western fears, has denied experts of the U.N.'s International Atomic Energy Agency permission to visit the Parchin site despite multiple requests from the agency this year. Tehran says a visit is possible only after extensive planning and a detailed outline of procedures — a caveat IAEA officials describe as a stalling tactic.

The agency said a new meeting was planned for Friday "to resolve issues relating to Iran's nuclear program," terminology similar to that describing previous such sessions related to Parchin.

IAEA chief Yukiya Amano has urged Iran to give access, saying wrecking crews at the site have removed buildings, moved soil and carried out other activities that "may hamper our future verification activities." He also has said that information about Parchin indicates activities "may have been undertaken related to the development of nuclear explosive devices," adding that early access "is very important to clarify this issue."

The alleged experiments at Parchin, which is located about 20 miles southeast of Tehran, are part of a broader skein of suspected activities that the IAEA has said point to attempts by Iran to develop nuclear weapons. Tehran says it is enriching uranium only to make reactor fuel and for scientific and medical research. But its refusal to accept enriched material from abroad and continue enrichment domestically despite stifling sanctions has strengthened fears it may want to use enriched uranium for its other purpose — the creation of nuclear missile warheads.

Earlier this year, the IAEA showed its 35 board member nations satellite images of the site that apparently showed suspicious activity. According to the diplomats who attended the closed meeting, the images showed that at least two buildings were razed and water streaming out of another structure suspected of hiding a metal chamber allegedly used to test explosives that could be used to set off a nuclear charge.

Commercial satellite images published subsequently by the Washington-based Institute for Science and International Security showed two buildings visible on earlier photos no longer standing, while later satellite photos published by ISIS showed more work on changing the topography of the site.

Asked Tuesday about the status of the alleged cleanup, a senior diplomat from a nation critical of Iran's nuclear program said that it had now entered the "end-phase."

The diplomat, who demanded anonymity because he was not authorized to discuss intelligence information, said his information was based on secret satellite imagery. He declined to discuss what the images showed because they were classified but suggested some of the work was now hidden from spy satellite view by screens set up over the site.

He and another diplomat said the agency could conclude in its Iran report due within the next few weeks that its chances of finding the smoking gun it seeks at Parchin are now minimal due to the alleged extensive cleanup. The second diplomat also demanded anonymity because he was not authorized to discuss confidential information with reporters.

Iran also has defied international pressure — and growingly severe U.N. and other sanctions — aimed at forcing it to curb uranium enrichment. Instead, it has increased the enrichment from grades used for reactor fuel to a level closer to what is needed to arm nuclear warheads.

Tensions have further been fueled by deep Israeli-Iranian enmity. Israeli leaders have been indicating impatience over Western diplomatic and economic moves to deter Iran and increasingly talk of attacking its nuclear facilities, though some analysts believe the saber-rattling is a bluff to increase pressure on Tehran. Iranian leaders have rejected Israel's warnings, threatening punishing retaliation

Because all enriched uranium can be further processed to weapons-grade material, Iran's nuclear secrecy has fed worries that it could quickly "break out" a weapons program.

"The comments of Israel's top officials suggest that its patience is wearing thin and that it may act soon, in weeks if not months," Eliott Adams, who served in foreign policy positions under presidents Ronald Reagan and George W. Bush, wrote in a recent commentary for The Foreign Policy Initiative.