The assertion came one day after the U.S. Navy launched a major exercise in the Gulf near the coast of Iran. The United States said the exercise did not mark preparations for any war against the Teheran regime. Saudi Arabia, a key U.S. ally, asserted that the United States has not conducted any wargames in the Gulf.

The Russian official said the Pentagon has been examining a range of scenarios to defeat Iran. He said that at this point no decisions have been made.

[On Wednesday, the government in Ankara was said to have rejected a U.S. request to expand air combat training in Turkey. Turkey's Cehan news agency quoted Turkish military sources as saying that the U.S. Defense Department sought Ankara's approval for a night air combat exercise.]

Russia has been regarded as Iran's leading ally. Moscow has rejected U.S. efforts to impose harsh sanctions on Iran, and Russian contractors have been helping Teheran's nuclear and missile programs.

This was not the first time that Russia warned of a U.S. attack on Iran. Last week, Col. Gen. Leonid Ivashov, vice president of the Academy of Geopolitical Sciences, said the United States was planning an imminent air strike on Iran's military infrastructure.

At the same time, Britain has escalated the war of words against Teheran in wake of the Iranian capture of 15 British Navy sailors in Shatt Al Arab on March 23. British Prime Minister Tony Blair, asserting that Iran entered Iraqi waters to abduct the sailors, said Britain and its allies would increase pressure on Teheran.

"It is now time to ratchet up the diplomatic and international pressure," Blair said.

British Foreign Secretary Margaret Beckett said the government has suspended all relations with Teheran. Britain has been a supplier of dual-use equipment to Iran's military and security forces.

"We need to focus all our bilateral efforts during this phase on the resolution of this issue," Ms. Beckett said. "We will therefore be imposing a freeze on all other official bilateral business with Iran."