Iran warned the United States yesterday not to attack its nuclear facilities and said talks with Europe might produce a deal to defuse the dispute over its alleged covert ambitions to build atomic weapons.

"They know our capabilities. We have clearly told the Europeans to tell the Americans not to play with fire," Iranian spokesman Hamid Reza Asefi told a news briefing in Tehran, referring to Washington's refusal to rule out the use of force.

Germany, however, warned that Iran could be referred to the UN Security Council for its nuclear activities - a toughening of the European line that narrows a rift between Europe and Washington which Iran has tried for months to exploit.

An American newspaper, meanwhile, reported that US military bases had been flying pilotless drone aircraft into Iran to hunt for tell-tale traces of nuclear weapons programmes.

Mr Asefi said Iran was determined to continue its nuclear programme which it says is solely for peaceful power generation.

But Washington accuses Tehran of secretly pursuing atomic weapons under cover of the civil programme and says it does not rule out any option to stop it acquiring them.

France, Britain and Germany have been trying to persuade Iran to scrap potentially weapons-related activities in return for economic incentives.