Vienna, Austria ? Iran has offered to stop some activities linked to uranium enrichment, diplomats said Tuesday. The United States said the move would not stop it from trying to have Tehran hauled before the U.N. Security Council for allegedly trying to make nuclear arms.

The diplomats, who spoke to The Associated Press on condition of anonymity, said Iran tentatively agreed to re-impose a freeze on making, testing and assembling centrifuges used to enrich uranium.

Uranium enriched to high levels can be used to make nuclear warheads. At lower levels, enriched uranium can generate power, the only activity Iran asserts it is interested in.

Iran last year agreed to freeze enrichment activities but has since resumed testing, assembling and making centrifuges. Last week it confirmed a report by the International Atomic Energy Agency — the United Nations’ nuclear watchdog — that it planned to convert more than 40 tons of raw uranium into uranium hexafluoride, the feed stock for enrichment.

The issue of enrichment is extremely sensitive as the international community tries to determine whether Iran is using its nuclear program for peaceful purposes or trying to make weapons.

U.S. officials are spearheading an effort at an IAEA board of governors meeting opening Monday in Vienna to have Iran declared in violation of the Nuclear Nonproliferation Treaty, a move that could force the U.N. Security Council to take action against Iran.

Enrichment does not fall under treaty obligations, but Tehran has been under international pressure for more than a year to fully renounce enrichment to counterbalance suspicions generated by nearly two decades of clandestine nuclear activities that came to light only two years ago.

Although Iran agreed to suspend its enrichment program almost a year ago, even that commitment — which fell short of a pledge sought by the international community to scrap enrichment — eroded over the subsequent months. Iran confirmed in July that it had resumed building nuclear centrifuges.

In Washington, Secretary of State Colin Powell brushed aside reports of Iran’s newest offer.

Powell said he “would be more interested in seeing Iranian action to stop the steps that they are now embarking upon with respect to the production of materials that, in our judgment, leads to nuclear weapons.”

While some European governments hoped to find a solution with Iran through diplomacy, “unfortunately I do not think the response from Iran has been very positive or constructive,” Powell said.

“Time is passing, and this is a matter that should go to the Security Council as quickly as possible,” Powell said, implying that there was need for economic, political or diplomatic sanctions against Tehran.