LONDON Ñ Iran has again escaped censure over its nuclear program, prompting the United States to warn it may take unilateral action against the Islamic regime at the UN Security Council, and in the form of sanctions.

The International Atomic Energy Agency's long-awaited resolution has failed to determine whether Iran violated its agreement to comply with United Nations nuclear inspectors.

On Monday, the IAEA board of governors instead adopted a resolution that welcomed Iran's decision to suspend uranium enrichment activities in an agreement with Britain, France and Germany.

"This is clearly a first step in the right direction," IAEA director-general Mohammed El Baradei said after the resolution was adopted.

"It will help mitigate international concern about the nature of Iran's program and over time should help to build confidence with regard to Iran's nuclear program."

The United States distanced itself from the resolution, passed by consensus. U.S. envoy Jackie Sanders said Washington has lost any illusion that Iran's nuclear program was peaceful and warned that the United States could act unilaterally.

"Quite apart from the question of how this board chooses to handle these matters, of course, the United States reserves all of its options with respect to Security Council consideration of the Iranian nuclear weapons program," Ms. Sanders said. "Any member of the United Nations may bring to the attention of the Security Council any situation that might endanger the maintenance of international peace and security."

The U.S. envoy said Washington would impose sanctions on any company that exports weapons-related equipment to Iran. She did not elaborate.

The IAEA resolution served Iran's aim to prevent the issue of Teheran's nuclear program from being relayed to the UN Security Council. Such a move could have resulted in sanctions on the Islamic republic.

Iran's agreement to suspend uranium enrichment was not legally binding, the resolution said. The agency said it would monitor 20 gas centrifuges in Iranian nuclear facilities that had been operating until the freeze.

Iran and the EU agreed to launch talks on Dec. 15 regarding incentives for Teheran to maintain its commitment to suspend uranium enrichment. The incentives were expected to include nuclear technology and trade benefits.

El Baradei told the 35-nation board of governors that the agency did not find any diversion of nuclear materials for Iranian weapons purposes. But he said he could not rule out a secret Iranian nuclear weapons program.

The resolution did not set any date for El Baradei to report to the board of governors. Since March 2003, El Baradei has reported to the board seven times.

Western and U.S. intelligence sources have maintained that Iran was continuing with a secret uranium enrichment program that has not come under IAEA monitoring. They said Iran has been conducting uranium enrichment in at least two Defense Ministry facilities in Isfahan and Teheran.

On Monday, the German news weekly Der Spiegel reported that since October Iran has been constructing a secret tunnel in an effort to continue uranium enrichment. The newspaper said the tunnel was being constructed in Isfahan on orders of Iranian supreme leader Ali Khamenei to ensure the concealment of Iran's nuclear weapons program.

Der Spiegel said the tunnel would house production of a large amount of uranium UF6 gas which can be enriched in gas centrifuges. Iran has denied the report.