Russia and the United States appeared to be on a collision course over Iran today after Moscow announced that it wanted to help Tehran’s new leadership to build six more nuclear plants.

The announcement followed reports this week that the Bush administration was considering imposing sanctions on Russian and other companies suspected of helping weapons programmes in Iran, Syria or North Korea.

Washington and Moscow have long been at odds over the involvement of AtomStroiExport and other Russian companies in constructing an $800 million, 1,000-megawatt nuclear reactor at Bushehr in southern Iran.

But tensions have escalated since the election of the conservative Mahmoud Ahmadinejad as Iran’s President, setting the stage for a tense confrontation at the G8 summit in Gleneagles next month.

Russia’s Foreign Minister, Sergei Lavrov, rejected US allegations that energy-rich Iran was using its nuclear energy programme as a cover to produce a nuclear bomb. "If we knew that Iran had plans of this kind, we would never have started cooperating with it in the nuclear sector," he said in interview with the al-Watan al-Arabi Arab weekly, a copy of which was posted on the Russian Foreign Ministry website.

"All assertions that Russia is allegedly facilitating the acquisition of nuclear weapons by Iran are absolutely unfounded."

In Moscow, the Federal Atomic Energy Agency chief, Aleksander Rumyantsev, said that Russia wanted to bid for contracts to build more reactors in Iran. "When Tehran announces new tenders to construct nuclear reactors, we’ll take part in them," he said. "Tehran intends to build another six nuclear reactors." He said the first power unit at Bushehr would be ready by 2006.

Analysts said that Russia was keen to establish good relations with the new Iranian leadership, to protects its status as an intermediary between Tehran and Washington, and to avoid losing out to competition from Europe. Britain, France and Germany have been negotiating a deal with Iran that would recognise its rights to develop nuclear energy for peaceful purposes and allow it greater access to international markets.

Mr Ahmadinejad has said that Tehran is determined to press on with its nuclear programme while continuing talks with the Europeans.

Konstantin Kosachyov, head of the Duma’s committee for international affairs, reacted angrily to Washington’s reported threat to target the US assets of Russian firms suspected of helping Iran’s weapons programme.

He said:"Russia should demand that the US partners produce comprehensive proof... If they fail to offer the data we will once again have to conclude that the US resorts to sanctions, firstly, as an instrument of pressure on disagreeable regimes, and secondly, as an instrument of dishonest competition against Russian companies."

US sanctions on Iran have also had an unintended consequence for cooperation in space between Washington and Moscow. With the shuttle fleet grounded, NASA must start paying to use Russian rockets to service the International Space Station from April next year, but is not allowed to under the Iran Non-Proliferation Act.

NASA’s chief, Michael Griffin, was forced to ask Congress this week to ease the law, which bans US entities from paying for transportation services from countries helping Iran’s weapons programme.

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