Hardline Revolutionary Guards have said they will crush any protests against the re-election of Iranian President Mahmoud Ahmadinejad. The threat comes as United Nations Secretary-General Ban Ki Moon urged Iranian authorities to stop using force against civilians, adding that they should respect civil rights in dealing with protesters. People in Tehran, in a gesture of defiance first used in the 1979 Islamic revolution and now adopted by pro-reform protesters, again chanted "Allahu Akbar" (God is greatest) from their rooftops on Monday night. Witnesses said supporters of opposition leader Mir Hossein Mousavi, officially beaten into second place by Mr Ahmadinejad in the June 12 presidential election which he says was rigged, had earlier gathered in Tehran's Haft-e Tir square. Residents said riot police, some on motorbikes, and members of the religious Basij militia were out in force. One witness said he had seen a group of protesters chanting slogans being attacked by the Basij, who dragged the demonstrators out of a nearby house to which they had fled. "The Basiji were really aggressive and swearing at me to go inside," said the witness. "I was scared they were going to break into my house too." The statement by the Revolutionary Guards - viewed as the most loyal guardians of the ruling clerical establishment - clearly signalled a crackdown on any new unrest. "In the current sensitive situation... the Guards will firmly confront in a revolutionary way rioters and those who violate the law," said a statement on the Guards' website. Ali Shahrokhi, head of parliament's judiciary committee, said Mr Mousavi should be prosecuted for "illegal protests and issuing provocative statements" after he called for new protests by his supporters on Sunday. Iranian authorities have accused Western powers of supporting the protests - the most widespread since the 1979 Islamic revolution - and have not ruled out expulsions of some European ambassadors. Sweden, the European Union's next president, said the bloc's members should consider drafting a plan to take in and provide aid to demonstrators at their embassies in Iran. Italy said it was prepared to open its embassy to wounded protesters. Meanwhile, Iran's Guardian Council has again ruled out any annulment of the June 12 presidential election, as demanded by two defeated candidates, state TV said. "Iran's Guardian Council rejects annulment of the June 12 presidential election, saying that there have been no major polling irregularities," it said.