"The elections are a matter for the Iranian people, but if there are serious questions that are now being asked about the conduct of the elections, they have got to be answered," Brown said in London.
He said there should be "no violence in response to peaceful protests".
"I think Iran has got to listen very carefully, because the relationship they will have and the respect they will have from the rest of the world will depend on how they respond to what are legitimate grievances that are being expressed and have to be answered," said Brown.
--IANS