ATHENS (Reuters) - A car bomb blew up outside the Athens stock exchange on Wednesday, damaging the building extensively and slightly wounding one woman, in what police suspect was a new attack by a leftist or anarchist group. The Athens bourse opened normally despite the blast, which blew out windows on several floors of the building and hurled debris hundreds of metres away, setting eight nearby vehicles ablaze. Police said a home-made bomb exploded at the same time outside a government building in the northern city of Thessaloniki, causing minor damage but no injuries. It was not clear if the two attacks were connected. Leftist and anarchist groups have carried out several attacks on police and businesses since December 2008, when the police shooting of a teenager sparked Greeces worst riots in decades. Police suspect one such group planted the bourse bomb. All evidence shows it was a terrorist attack, said police spokesman Panayiotis Stathis, as anti-terrorist police gathered evidence from the cordoned-off area and checked video footage. We have no claim of responsibility yet. An anonymous caller warned a Greek newspaper of the attack, whose apparent aim was to damage the building but not people. The injured woman was a cleaner working in a nearby building. Police said the makeshift time bomb contained about 15kg of explosive material, planted in a white van on a side street beside the exchange. A nearby car dealership, other businesses and four apartments were also damaged. Inside the stock exchange, offices were strewn with broken glass and desks covered with debris, Reuters TV images showed. Its the biggest amount of explosives planted in a car ever to blow up in Greece, said a police official who declined to be named. Police said the bomb resembled those planted by the leftist Revolutionary Struggle, Greeces most militant group, which emerged in September 2003 after the capture of the November 17 group. In 2007 it fired a grenade at the US embassy, hitting its facade, and earlier this year it shot and seriously wounded a police officer outside the Culture Ministry. The Athens stock exchange opened at 0730 GMT and stocks were trading down by 1.44 percent at 1345 GMT. Athens and Nicosia share a trading platform. The major blast that occurred outside the Athens exchange has hurt the building but that has not affected at all the operation of our market, Athens Stock Exchange Chairman Spyros Kapralos told Reuters. Leftist and anarchist guerrilla groups have claimed responsibility for several attacks this year on businesses, cars and police, culminating in the assassination of a policeman in his car in June by the Rebel Sect group. Imitating the November 17 group, which killed 23 Greeks and foreigners in 27 years but avoided hurting bystanders, other Greek guerrilla groups usually strike at night when businesses are closed to avoid alienating the public.