Iran's top legislative body has said it is ready to hold a recount in the hotly-contested presidential poll. The election was won by hardline incumbent Mahmoud Ahmadinejad, but defeated candidate Mir Hossein Mousavi has criticised his re-election, claiming widespread fraud. Mr Mousavi has appealed to the Guardian Council for the election to be annulled, but has said he is not optimistic about its verdict. The council, however, said the recount may lead to changes in candidates' tally. On Monday, seven people were killed and many others wounded in the mass protests held in the Iranian capital Tehran. They were killed near a rally held by supporters of Mr Mousavi as they prepared for more protests against an election they say was rigged. The deaths occurred at the end of Monday's rally - a mainly peaceful gathering attended by many hundreds of thousands of people - when "thugs" tried to attack a military post in central Tehran. An Iranian photographer at the scene said Islamic militiamen opened fire when people in the crowd attacked a post of the Basij religious militia. The Iranian capital has already seen three days of the biggest and most violent anti-government protests since the 1979 Islamic revolution, and Mr Mousavi's supporters have pledged to continue their demonstrations. "Tomorrow at 5pm at Vali-ye Asr Square," some of the crowd chanted at Monday's march, referring to a major road junction in the sprawling city of some 12 million. And in a move that could raise the possibility of further clashes between the rival camps, backers of hardline Iranian President Ahmadinejad said they are also planned a demonstration at the same location as Mr Mousavi's supporters. Further protests, especially if they are maintained on the same scale, would be a direct challenge to authorities who have kept a tight grip on dissent since the US-backed shah was overthrown after months of demonstrations 30 years ago. US President Barack Obama said he was "deeply troubled" by post-election violence in Iran. "The democratic process, free speech, the ability of people to peacefully dissent - all those are universal values and need to be respected," he said. The US and its European allies have been trying to engage Iran and induce the world's fifth-biggest oil exporter to halt nuclear work that could be used to make an atomic bomb. Iran says it only wants nuclear energy to generate electricity. Mr Obama said he would continue pursuing tough, direct dialogue with Tehran but urged that any Iranian investigation of election irregularities be conducted without bloodshed. The world was inspired by the Iranian protesters, he said. Demonstrators filled a broad avenue in central Tehran for several miles on Monday, chanting "We fight, we die, we will not accept this vote rigging", in support of Mir Hossein Mousavi, the defeated moderate candidate. Mr Mousavi said he was "ready to pay any price" in his fight against election irregularities. Some formed a human chain in front of a building of the Basij Islamic militia, but others broke through and the hardline volunteer paramilitaries opened fire on the crowds sending thousands fleeing in havoc. "Tanks and guns have no use any longer," chanted the protesters in a deliberate echo of slogans used leading up to the 1979 revolution. Members of Iran's security forces have at times fired into the air during the unrest and used batons to beat protesters who have pelted police with stones. The Basij militia is a volunteer paramilitary force loyal to Supreme Leader Ayatollah Ali Khamenei who has the final say on all matters of state in Iran. Gunfire was also heard in three districts of wealthy northern Tehran on Monday evening and residents said there had also been peaceful pro-Mousavi demonstrations in the cities of Rasht, Orumiyeh, Zahedan, and Tabriz.