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.
(Reporting by Matt Falloon; editing by Elizabeth Piper)
