Russia has been helping Iran build the plant in the southern city of Bushehr since the mid-90s but its launch has been marred by a series of delays and the issue is hugely delicate amid a standoff over Iran's nuclear programme.

"The launch of the first unit of Iran's nuclear power station should be implemented already this summer," Putin was quoted as saying by Russian news agencies at a meeting on nuclear industry matters in the city of Volgodonsk in southern Russia.

Putin's comment represented one of the clearest recent statements by a Russian official about when the controversial facility will finally come online.

Tehran is accused by the West of planning to build a nuclear bomb although it insists its nuclear drive is purely peaceful in nature.

Vladimir Pavlov, an official with Russia's nuclear contractor Atomstroiexport overseeing the construction of the Iranian nuclear plant, said the launch was planned for July, the Interfax and Ria-Novosti news agencies reported from Volgodonsk.

Trial runs would start in April, when major equipment would be tested, Pavlov said.

Putin's announcement drew an immediate reaction of concern from US Secretary of State Hillary Clinton, who has been looking over the past year for Russia to take a tougher line on Iran.

"We have consistently said that Iran is entitled to civil nuclear power," she said at a news conference with her Russian counterpart Sergei Lavrov in Moscow.

"It is a nuclear weapons programme that it is not entitled to and if it reassures the world, or if its behaviour has changed because of international sanctions, then it can pursue peaceful nuclear power."

"In the absence of these reassurances, we think it would be premature to go forward with any project at this time because we want to send an unequivocal message to the Iranians," she said.

Clinton said the Iranian nuclear programme "remains an issue of grave concern for the international community".

"We are as committed as we have been to a diplomatic solution, but there must be a solution. Iran is not living up to its international obligations."

At the meeting, Putin tasked officials with boosting Russia's share on the global nuclear market to 25 percent from the current 16, saying Russia was designing and building 15 nuclear power reactors at home and abroad.

"We have a solid set of orders but we need to move forward," Putin said in televised remarks.

"I believe that we are quite capable of occupying no less than 25 percent of the global market for the construction and maintenance of nuclear power stations," he said, estimating Russia's current share at 16 percent.

Russia is constructing or gearing up to construct nuclear reactors in a host of countries, including China, India and Bulgaria and Putin said the country was in talks to build more nuclear units in Turkey, Armenia and several other countries he did not identify.

"We are ready to invest in the construction of energy units in those countries that have changed legislation and now allow foreign capital in nuclear stations," Putin said.

His lightning trip to New Delhi late last week yielded a broad agreement that foresees the construction of up to 16 nuclear reactors at three Indian sites in the coming years, a major triumph for Russia's state atomic agency Rosatom which faces stiff competition in the country from French and US rivals.

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