Video footage has emerged appearing to show the moment Iranian protesters were shot dead by a gunman. The amateur film, which was posted on YouTube, shows someone leaning out of a window of a compound with a gun as demonstrators gathered outside. It comes as the British Ambassador to Tehran was summoned to the Iranian Foreign Ministry. It is believed the Iranian authorities were angered by remarks made by Prime Minister Gordon Brown and Foreign Secretary David Miliband. Mr Miliband said: "The most fervent hope is for peaceful protest to be met with peaceful response from the state authorities. "The loss of life that's happened - the seven that have been reported, the credible reports of greater loss of life - are to be deplored very clearly." It is believed seven people were killed in Tehran's Azadi Square at a rally held in support of the main opposition candidate Mir Hossein Mousavi. His defeat to hardline incumbent Mahmoud Ahmadinejad in the Iranian election has prompted widespread anger and more protests are planned for later. Foreign media have had massive restrictions put on them so footage and information is coming from social networking and video sharing websites. The country is witnessing the biggest demonstrations since the 1979 Islamic revolution. State television has said the "main agents" in the unrest have been arrested with explosives and guns but gave no further details. A Culture Ministry official said of the media clampdown: "No journalist has permission to report or film or take pictures in the city." Meanwhile, Iran's top legislative body, the 12-man Guardian Council, has refused to annul the poll but says it is "ready to recount the disputed ballot boxes claimed by some candidates, in the presence of their representatives".