A military strike on Iran's nuclear facilities would be "a mistake", the European Union's foreign policy chief, Javier Solana, has warned.
Solana said any unilateral military action would be counterproductive
"That will complicate enormously the situation," he told Britain's ITV television network.
US Secretary of State Condoleezza Rice said last week a strike on Iran was "not on the agenda at this point".
Ms Rice also urged Europe to show "unity of purpose" with Washington in opposing Iran's nuclear programme.
The US accuses Tehran of trying to develop nuclear weapons. Iran has repeatedly denied the charge, insisting that its nuclear programme is for civilian use.
The EU has been negotiating with Tehran over its nuclear activities, but the US has urged a tougher stance.
France, Germany and Britain are trying to persuade Iran to turn a freeze on its nuclear enrichment activities into abandonment.
'Difficult to conceive'
Mr Solana was interviewed on ITV's Jonathan Dimbleby programme, to be for broadcast on Sunday.
Asked about US Vice-President Dick Cheney's warning last month that Israel might attack Iran's nuclear facilities without warning, Mr Solana said: "I think that would be something I would not like to see taking place.
"That would be a mistake. That will complicate enormously the situation."
"Unilateral action of that nature I don't think will contribute to what is the aim of everybody... I don't think at this point in time that it is worth thinking about that".
Asked if he agreed with UK Foreign Secretary Jack Straw that a US military action against Iran was "inconceivable", Mr Solana replied: "I think at this point in time military action... is very difficult to conceive.
"I don't think that the United States has at this point of time the wish or the will or the capability to do that," Mr Solana said.
He was speaking as Ms Rice continued her first major European and Middle East tour since being confirmed as the new US secretary of state.