The UK Foreign Office urged Iran not to take unilateral steps that could jeopardise talks with three European Union nations - known as the E3.
The remarks came after a top Iranian official set a Sunday deadline for the EU to propose economic incentives.
The UK - the current EU president - said these would be given in a week.
This was in accordance with the decisions of the Geneva meeting in May between Iran and the three European countries - Britain, France and Germany - as well as the EU's foreign policy chief, Javier Solana, said a Foreign Office (FCO) spokesman.
This is threatening to become a dangerous escalation, says the BBC's Jon Leyne.