A report by a U.N. agency that there is "credible" evidence that Iran is working to design a nuclear weapon has spiked the decibel level of concern in world capitals.

EU officials in Brussels say preliminary discussions among members on possible new sanctions on Tehran are under way and plans for imposition of economic punishments could be ready by Dec. 1, when EU foreign ministers are to meet.

"We cannot accept this situation, which is a threat," French Foreign Minister Alain Juppe said, adding that France is prepared to impose unprecedented sanctions.

British Foreign William Hague warned that no option is off the table to deal with the issue. In Washington, the White House appears to be avoiding a war of words with Tehran but an unidentified official is reported as saying the report released this week is "comprehensive, credible, quite damning and alarming."

In Israel, speculation has been rife for weeks over a possible pre-emptive military strike against Iran's nuclear facilities. Israeli Prime Minister Binyamin Netanyahu simply noted the report "corroborates the position of the international community, and of Israel, that Iran is developing nuclear weapons."

Rumor that the report by the International Atomic Energy Agency would be far more explicit in detail and damning in conclusions preceded its release. Yet when presented to the public, it still hit with a splash.

The agency said it had credible evidence that Tehran -- despite assertions to the contrary -- has sought to design a nuclear warhead and even conducted computer modeling in 2008 and 2009 on an explosion of such a device.

It also disclosed that Iran has been transferring nuclear material to an enrichment site in a mountain where it would be safe from any possible military strike by Tel Aviv, which in the past attacked Iraqi and Syrian nuclear program sites.

Iran's nuclear weapons program, it indicated, may be ongoing.

Iran, for whom Moscow has built at least one reactor site for uranium enrichment, has for nearly a decade insisted its activities were peaceful and designed for civilian energy needs.

Any suspicions to the contrary were heighted in 2002 when an Iranian dissident group revealed the existence of two nuclear sites in Iran that Tehran had kept secret, in violation of international proliferation agreements. Yet there was no evidence of Iran, despite its violation of IAEA strictures, was pursuing a nuclear weapons program.

The latest and strongest IAEA report in effect jells earlier doubts in Western countries, which have been negotiating with Iran for years.

The United States, EU countries and the United Nations have imposed economic sanctions on Iran as a result of its violation of international nuclear activity agreements. They include the freezing of assets of more than 200 Iranian entities tied to Tehran's nuclear activities and the freezing of assets of some 35 people.

Western nations, which are expected to tighten the screws, are also expected to call for stronger sanctions being imposed by the U.N. Security Council. Russia and China, which hold veto power on the council, however, oppose tighter sanctions against Tehran and could scupper such a move.

Tehran reacted to the new report as expected. It denounced it as false, as propaganda by Israel and the United States.

Iranian officials, who said Iran would not stop its "peaceful" nuclear program, also repeatedly warned that any military action undertaken against the country would have dire consequences for those involved.

In its report, the IAEA didn't give any timeline on when Tehran could actually possess nuclear warheads but speculation in capitals around the world have spanned periods of months or just a few years.