Grenade-throwing gunmen attacked a gold mining town and surrounding ranches in northern Colombia, killing at least 34 civilians and leaving 31 people injured, authorities said Saturday.

The state governor and an army general said 200 leftist guerrillas carried out the attack, but a local mayor claimed it was done by dozens of members of a right-wing death squad.The gunmen rode into Segovia during a thunderstorm Friday night and blasted the telephone exchange, city hall, the main park, two bars and a commercial establishment, authorities said.

"It was an ordinary weekend, with people talking in the park, drinking in the bars, listening to music and enjoying themselves when this criminal act was perpetrated, bringing pain and sadness to many homes," Antonio Roldan Betancur, governor of Antioquia state, told radio networks Caracol and RCN on Saturday.

Authorities first reported that an army post also was attacked, but RCN, without citing sources, later said it learned the army post was not attacked.

Segovia Mayor Rita Tobon Areiza, of the leftist Patriotic Union Party, said gunmen first attacked ranches near the town and that casualties outside of town could raise the death toll to 50.

The mayor, interviewed by RCN, did not say if the gunmen were guerrillas or a death squad.

Betancur said the gunmen belonged to the leftist National Liberation Army and the Revolutionary Armed Forces of Colombia.

Leftist guerrillas have been fighting to overthrow the government for 25 years and establish a Marxist state.