VIENNA (AP) - The U.S. and Europe said Wednesday they share U.N. fears that Tehran may be secretly working on developing nuclear missiles, expressing support for new sanctions if Tehran continues to defy Security Council demands.

Their comments reflected the change in tone of the International Atomic Energy Agency under new director-general Yukiya Amano in its assessment of Iran's nuclear ambitions.

Amano, in a recent report prepared for this week's board meeting, expressed the possibility that Iran may be working on making a nuclear warhead, with the IAEA suggesting for the first time that Tehran had either resumed such work or never stopped three years ago, as thought by U.S. intelligence agencies.

Iran denies any interest in developing nuclear arms. But the report said Iran's resistance to agency attempts to investigate for signs of a nuclear cover-up "give rise to concerns about possible military dimensions to Iran's nuclear program."

An unusually strongly worded statement delivered by Spanish IAEA chief delegate Jose Luis Rosello on behalf of the EU to the IAEA's 35-nation board criticized Tehran on a wide range of issues linked to concerns that its nuclear program may be a front for clandestine efforts to make atomic warheads.

"The EU shares the agency's concerns about the possible existence in Iran of past or current undisclosed activities related to the development of a nuclear payload for a missile," according to the statement.

Beyond making the same point, U.S. chief delegate Glyn Davies said the IAEA is justified in being concerned that Tehran - accused of repeatedly concealing suspicious nuclear activities or revealing them only to pre-empt being found out - "about the possible construction in secret of other new nuclear facilities in Iran."

Iran became the focus of an IAEA investigation in 2002 after revelations that it was clandestinely assembling an enrichment program through black market access to technology and know-how and since then has been frequently criticized by the West of stonewalling the agency - an issue touched on by Davies, who accused Iran of playing a "cat and mouse game."

"We find ourselves eight years into an investigation which Iran seems determined to defy, obfuscate, and stymie," he said. "The list of outstanding issues has grown and become even more alarming."

Iran is weathering three sets of Security Council sanctions meant to punish its refusal to freeze its uranium enrichment program, which can be re-engineered to produce highly enriched, weapons grade uranium instead of its present low-enriched output.

It insists that it is enriching only to produce fuel for an envisaged nuclear network.

But it has recently rejected a plan that foresaw shipping out most of its enriched stockpile and having it returned as fuel for a research reactor producing medical isotopes, deciding instead to start enriching domestically to higher levels in what is says is a move to produce the fuel on its own - something the West says it lacks the technology for. That, plus its belated acknowledgment that it had been secretly building a new enrichment facility, has increased sentiment for new sanctions.

The U.S., Britain and France support such a measure, and Russia - which is normally opposed - appears to be moving closer to embracing the Western view, leaving only fellow permanent Security Council member China - which depends on Iran for much of its energy needs - opposed.

The Security Council's five permanent members have veto power, so China could block council sanctions, although it is more likely to abstain if the other four are in support.

Wednesday's EU statement also expressed support for new U.N. Security Council "action" if Iran continues its nuclear defiance - diplomatic language for a fourth set of U.N. sanctions.

Davies, too, said the international community has "no choice but to pursue further, deeper sanctions to hold Iran accountable" if it persists in shrugging off Security Council demands. In Geneva, German Foreign Minister Guido Westerwelle said sanctions could not be ruled out if Iran continues "to refuse dialogue and transparency."

U.S. Secretary of State Hilary Clinton told Congress last week that she expected new sanctions were only 30 to 60 days away, but on Monday she seemed to roll back that timeline, saying only that she thought they would be considered "in the next couple months." The comment seemed to reflect difficulties in winning unanimous support for sanctions.

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Associated Press writers Eliane Engeler in Geneva and Alexander Mueller and Noura Maan in Vienna contributed to this report.