Mahmoud Ahmadinejad, center, arrives in Minsk, Belarus, 21 May 2007

Iran's President Mahmoud Ahmadinejad has vowed to push ahead with his country's nuclear program, despite a United Nations Security Council deadline Thursday for Tehran to stop enriching uranium.

Iranian media quote Mr. Ahmadinejad as saying if Tehran halts its atomic program even for a moment, then countries opposed to it will have achieved their goals.

At the White House, President Bush said the U.S. will work with its allies to strengthen sanctions against Iran. He said Iran continues to defy the demands of the free world, which he said will only isolate Iran further.

Also Thursday, the head of the U.N. nuclear agency, Mohamed Elbaradei, voiced concern about Iran's growing nuclear capacity and said Tehran is three to eight years away from producing a nuclear weapon.

Wednesday, Elbaradei's International Atomic Energy Agency issued a report saying Iran has defied international demands by expanding uranium enrichment - a process that can make fuel for nuclear weapons.

The IAEA also said its ability to monitor Iran's nuclear program has been hurt by a lack of access. Iran says there are no obstacles for legal IAEA inspections of Tehran's nuclear facilities.

Iran is already under limited sanctions for ignoring earlier Security Council resolutions.

The United States and its allies accuse Iran of trying to develop nuclear weapons. Iran says its atomic program is intended to produce electricity.