YEREVAN (Combines Sources)–Thousands of opposition supporters have rallied in Yerevan demanding the impeachment of President Robert Kocharian and warning of fraud in parliamentary elections on May 12. Demonstrators marched to the headquarters of Armenia’s National Security Service to protest against the arrest this week of opposition leader and former Foreign Minister Alexander Arzumanian on money-laundering charges. Armenian authorities threatened on Thursday to prosecute organizers of the previous nights opposition demonstration in Yerevan that was marred by violent clashes between some of its participants and security forces and heightened political tension ahead of Saturdays parliamentary elections. The violence broke out when thousands of supporters of Armenia’s most radical opposition groups approached the Yerevan headquarters of the National Security Service to demand the release of a prominent opposition politician arrested by the former KGB earlier this week. Eyewitnesses said riot police used batons and tear gas to keep the crowd from moving too close to the NSS building and its basement jail whether the politician, Arzumanian, is being kept. Several opposition activists and police officers were reportedly injured in the melee that underscored the potential for post-election unrest in the country. Witnesses said the police briefly detained at least one demonstrator on the spot but had to release him to avoid a more serious confrontation with the angry protesters. Chanting Victory! and Freedom! the crowd then continued its march through the city center and ended in a brief rally in Liberty Square. The organizers of the protest, the opposition Republic and New Times parties and the Impeachment bloc, urged supporters to assemble in the same place on Sunday for what they hope will be a campaign of sustained anti-government protests. Victory is not achieved at once, said Nikol Pashinian, a firebrand Impeachment leader. Victory is achieved step by step. Today we took a very important step towards our victory. Well done. The deputy chief of the Armenian police, Major-General Ararat Mahtesian, charged the next morning that the clashes were deliberately instigated by radical opposition leaders and Pashinian in particular. Several participants led by Nikol Pashinian provoked an incident with police, dashed to the National Security Service entrance, and when police tried to stop their movement, scuffles broke out, he told a news conference. We have video of disobedience and collective hooligan acts committed by participants of the march, Mahtesian said, adding that three of his officers needed medical treatment afterwards. Mahtesian also said state prosecutors preparing materials to give the incident a legal evaluation. He emphasized the fact that the opposition march, which followed a rally held by Republic, New Times and Impeachment in another downtown Yerevan square earlier on Wednesday, was not sanctioned by city authorities. Mahtesian admitted that tear gas was used during the clash but implicitly claimed that it was sprayed by oppositionists. In that turmoil we were not able to ascertain whether tear gas was used by police officers or civilians, he said. Police officers themselves suffered from tear gas. It was sprayed in their direction. The police general went on to warn the radical opposition against staging similar demonstrations in the wake of the elections. Any manifestation of unlawfulness will be prevented and decisive measures will be taken against those who will try to destabilize the situation, he said. President Robert Kocharian issued a similar warning late last month.