Iran’s Revolutionary Guards have taken the extraordinary step of cutting down thousands of trees in Tehran to prevent U.N. inspectors from finding traces of enriched uranium from a top-secret nuclear plant.

According to Western intelligence sources, more than 7,000 trees that may have contained incriminating nuclear traces have been lost in a popular parkland area in the city near the Lavizan atomic research center.

At today’s meeting, the IAEA head, Mohamed ElBaradei, is expected to deliver a scathing report on Iran’s nuclear program. But Mr. ElBaradei will inform the board that he is not in a position to assert that the nuclear program is “entirely peaceful,” and blames Tehran for its lack of “transparency.”

Iran threatened to begin large-scale uranium enrichment if the IAEA formally refers it the Security Council. The Islamic republic’s top nuclear negotiator, Ali Larijani, told a press conference: “Research and development is in our national interest and Iran will not go back on that. If they [America and allies] want to use force, we will pursue our own path.”

One of the IAEA’s key concerns has been the government’s conduct over the Lavizan complex. The IAEA only became aware of its existence after Iranian exiles provided details of its location at a military base in Tehran in 2003.

Iran was accused of using the facility to conduct research into nuclear enrichment, and Israeli military officials claimed that the prototypes of four nuclear warheads were also stored at the site.

Western intelligence officials believe the site was deliberately situated in a major population area to make it more difficult for America and Israel, which are determined to prevent Iran developing nuclear weapons, from carrying out pre-emptive air strikes.

The Iranians responded to the exiles’ disclosure by razing the complex in 2004 before IAEA inspectors could conduct a full investigation.

To ensure that no incriminating traces of nuclear activity were found, they even plowed the site and removed 6 inches of topsoil.

Despite these efforts, IAEA inspectors still found traces of enriched uranium in soil collected from the site. Intelligence officials concluded that the traces came from nuclear equipment acquired from A.Q. Khan, the “father” of Pakistan’s nuclear bomb.

Recent tests in the area by scientists working for the Atomic Energy Agency of Iran showed unusually high concentrations of uranium contamination in the leaves and branches of trees surrounding the site. The scientists unanimously recommended that preparations should be made in case IAEA inspectors decided to conduct further visits.

The order to cut down the trees was given by the mayor of Tehran, Mohamed Baker Khalibaf, who is close to President Ahmadinejad. The official explanation for the destruction of the trees was to create a national park.

“The destruction of the trees is yet another example of the measures the Iranians are prepared to take to conceal the true nature of the nuclear program,” a senior Western official said.

“But after three years of deliberately trying to conceal their activities from the IAEA, none of the member states is prepared to give them the benefit of the doubt,” the official said.