Police in Thessaloniki have stepped up patrols seeking what they believe to be a small group of left-wing students deemed responsible for a bloodless string of gas-canister bomb attacks in the northern city over the past year. The latest attack, involving three bombs, targeted the city’s central town-planning offices early on New Year’s Day. Nobody was hurt, although the bombs caused some damage. Offices used by Greece’s largest parties, PASOK and New Democracy, have been hit in the past, together with banks and branches of the civil service. A police source told Kathimerini yesterday that, according to existing intelligence, the perpetrators are probably a small group of left-wing students. Witnesses have mentioned seeing a young couple at sites just before bombs went off. «This is not something organized with a broader scope,» the source said.