Leftist guerrillas attacked two towns Saturday, and officials said 21 people were killed in the fighting. They said it was one of the bloodiest rebel offensives in three decades of fighting.

The insurgents belonged to the country's two most active guerrilla groups, the Revolutionary Armed Forces of Colombia and the National Liberation Army, the army said. The two bands have carried out joint attacks against the army and police in recent months.An army statement said about 1,000 rebels launched dawn attacks on the towns of Taraza and Caceres in northern Colombia. The statement said at least 14 rebels, six soldiers and a police officer were killed. Another 15 were wounded, it said.