TEHRAN (AFP) - Riot police armed with steel clubs fired tear gas to break up an opposition rally in Tehran on Monday, witnesses said, as demonstrators defied a Revolutionary Guards threat to crush further protests over the disputed presidential election. The White House meanwhile deplored the lack of justice in Iran despite an appeal from President Barack Obama to the Tehran government to avoid violent and unjust actions towards its people. Obamas spokesman Robert Gibbs said that it was clear following scenes of violence from Iran over the weekend that justice has not been achieved. In Tehran, police backed up by the Basij force arrested up to 60 people as about 1,000 demonstrators gathered in Haft-e Tir Square, a popular shopping destination in the heart of Tehran, a witness said. One witness said helmeted police wielding steel clubs and cables, some on motorbikes, fired at least seven rounds of tear gas to disperse protesters. Rights watchdog Amnesty International urged Iran in a statement to stop using Basij force to police demonstrations, saying they have reportedly used excessive force against protesters. Defeated reformist candidate Mehdi Karroubi called for a ceremony to be held on Thursday to mourn protesters slain in demonstrations. State radio said at least 457 people had been detained in street clashes in Tehran on Saturday that left 10 people dead, bringing the overall toll from a week of violence to at least 17. Opposition leader Mir Hossein Mousavi, who has led massive protests over what he says was a rigged election that returned Mahmoud Ahmadinejad to power, urged supporters to continue demonstrating but adopt self-restraint to avoid more bloodshed. Election watchdog the Guardians Council acknowledged some discrepancies in the June 12 vote but insisted they would not effect the outcome, while the opposition is insisting not on a recount but a new vote. Since the turmoil began, Iranian security forces have cracked down on demonstrators and arrested many hundreds of protestors as well as prominent reformists, journalists and analysts. Mondays rally was reportedly called to pay tribute to Neda. The foreign media is banned from covering demonstrations, effectively keeping their journalists off the streets, but Iranians have been using social networking sites such as Twitter to get news to the outside world. The foreign ministry denounced the BBC and Voice of America as Israeli agents who aim to weaken the national solidarity, threaten territorial integrity and disintegrate Iran. Four student unions are planning demonstrations outside the British embassy on Tuesday to protest at interference by Britains perverted government. The Fars news agency quoted Esmail Tahmouressi, a student leader, warning that it could be another November 4, the date when some students seized the US embassy in Tehran after the 1979 revolution. Iran has ordered the BBC correspondent to leave and MPs called for Tehran to review its often strained relations with London. British Foreign Secretary David Miliband rejected charges that protesters were being manipulated by foreign nations and denounced what he said were Irans efforts to turn the election dispute into a battle with the outside world. Canadian Prime Minister Stephen Harper called on Iran to halt its assault on press freedoms and release all political prisoners and journalists. The 12-member Guardians Council said the number of ballots cast in 50 of the total 366 electoral districts exceeded the number of eligible voters. But spokesman Abbasali Kadkhodai said there were no irregularities and insisted any recount will not change the election outcome much. Ahmadinejad, who had put Iran on a collision course with the West during his first four-years with his anti-Israeli tirades and defiant stance on the countrys nuclear drive, was declared the victor with 63 percent of the vote. Mousavi, Karroubi and the third defeated challenger Mohsen Rezai have listed a total of 646 irregularities.