Drug gangs set fire to buses and opened fire on police stations and posts around Rio de Janeiro early Thursday in a wave of violence that killed 18 people, the state's top law enforcement officer said. The victims included seven who were burned to death in one of four torched buses and two policemen, said Roberto Precioso, head of Rio's Public Safety Department. Two other civilians were gunned down, including a street vendor caught in the crossfire of a shootout in Rio's Botafogo district, he said. Seven alleged gang members were also killed. Precioso said gang members used handguns, machine guns and grenades in 12 attacks against police stations and outposts that began in the early morning. Fourteen civilians and eight police officers were injured, he added. Precioso said the attacks were apparently a show of force staged before a new governor is sworn in on Jan. 1. Police intelligence had warned the gangs were planning the attacks for some time. "It is very difficult to prevent these types of attacks that were practically kamikaze," Precioso said at a news conference. "Police action prevented the situation from getting much worse."