In their biggest offensive of the year, leftist guerrillas attacked two adjacent towns in northern Colombia and about 40 people were killed, authorities said.

The army and police drove back some 1,000 members of two guerrilla groups who together attacked the towns of Taraza and Caceres in northern Colombia Saturday, the Antioquia state government said Sunday.Nine soldiers and 16 guerrillas died in the five-hour gun and mortar battle in Taraza, 250 miles north of Bogota. Eight soldiers were also wounded before the rebels were driven back into the mountains, the government said in a statement.

Authorities said Saturday's attacks were carried out by the country's two active guerrilla groups.