"Any military action near our border is unacceptable. We will take that extremely negatively and everything we can to oppose it," said Andrei Denissov, at a press conference, the Interfax agency reported.

Russia has no land border with Iran. But it is one of several countries that shares part of the Caspian Sea shoreline with the Islamic republic -- along with the former Soviet republics of Azerbaijan, Turkmenistan and Kazakhstan.

Asked if Russia was worried about possible US air strikes against Iran, he answered: "Yes, of course."

Meanwhile Russia's chief of staff, General Yuri Baluyevski, said any military strike against Iran would be a serious political mistake and would not give victory to the United States.

Washington has been building up its naval military presence in the Gulf further south.

It now has two aircraft carrier battle group in the region, the strongest US military presence there since the 2003 invasion of Iraq.

Washington has persistently denied reports that it is planning air strikes against Iran.

But US Vice President Dick Cheney, commenting on the crisis over Iran's nuclear programme, said last February: "It would be a serious mistake if a nation like Iran were to become a nuclear power."

He added: "All options are still on the table."

Washington suspects that Iran's civilian nuclear programme will be used to develop a military nuclear capability.

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