Iran must prove it is not interested in developing nuclear weapons, Prime Minister Gordon Brown said on Sunday.
Iran says it only wants nuclear technology for energy purposes but others suspect Tehran desires a nuclear arsenal, sparking speculation of a military confrontation and helping to drive oil prices to record levels above $140 a barrel this year.
"Iran has not been totally honest with the international community," Brown told CNN in an interview.
"We need a firm and absolute commitment that Iran is not going to break from the Non-Proliferation Treaty and have nuclear weapons. That is the first stage."
The United States and European Union have said they want to find a diplomatic solution to the stand-off, but Iran has so far ruled out halting its atomic programme in exchange for economic incentives.
