Militants ambushed a bus carrying Afghan construction workers in the country's volatile south, killing 19 of the laborers Friday after attacking them with a roadside bomb and gunfire, the Interior Ministry said.

CountryWatch: Afghanistan

The attack shortly after noon in Kandahar province began when a roadside bomb exploded near the bus, said Zemeri Bashary, the Interior Ministry spokesman.

Some of the laborers may have been killed by the bomb, while others were shot by militants who attacked the panicked workers with gunfire, he said.

Nineteen construction workers were killed in the attack and three wounded, Bashary said. It wasn't immediately known how many people were on the bus or who the laborers worked for.

The attack, in Shorabak district, occurred in a remote area of southern Kandahar province that borders Pakistan some 110 miles south of Kandahar city.

Southern Afghanistan has seen a surge of violence this year, fueled by a resurgent Taliban and a growing drug trade. Afghan officials say that Taliban fighters cross the border from northern Pakistan to launch attacks in Afghanistan.