"There is a likelihood of military escalation of the conflict, towards which Israel is pushing the Americans," Nikolai Patrushev, who heads the Kremlin's Security Council, told Interfax news agency.

Patrushev, a former head of the main successor to the Soviet-era KGB, said Tehran could respond by blocking the Strait of Hormuz between Oman and Iran, through which 35 percent of the world's seaborne traded oil passes.

"It cannot be ruled out that the Iranians will be able to carry out their threat to shut exports of Saudi oil through the Strait of Hormuz if faced with military actions against them," Patrushev said in an interview published on Thursday.

Tension over Iranian uranium enrichment, which has moved to a mountain bunker better protected from possible air strikes, has raised fears for world oil supplies and even of war.

Iran says its nuclear program is peaceful while Western powers believe it has military aims. Israel, which sees an Iranian atom bomb as a threat to its existence, is willing to attack Iranian nuclear sites with or without U.S. backing.

However, Patrushev said there was still no proof that Iran was on the brink of creating nuclear weapons.

"Talk about Iran creating an atomic bomb by next week we have heard for many years," he said, adding that the United States was trying to topple the Iran's leadership using "all available means" to make the country into "a loyal partner".

Russia, the world's biggest energy producer, opposes further U.N. Security Council sanctions over Tehran's nuclear program and has sharply criticized U.S. and European Union sanctions.

The United States has said it would use force if Iran carried out its threat to block the strait and moved a new aircraft carrier strike group to the Arabian Sea this week.