HEART: Twenty civilians were killed and another 27 injured when a crowded bus hit a Taliban-style roadside bomb in southwestern Afghanistan early Wednesday, an official said.

The bus was travelling on a highway in the Delaram district of Nimroz province when the blast occured, provincial governor Ghulam Dastgir Azad said.

"The roadside bomb struck a civilian bus this morning. Twenty civilians were killed and another 27 have been injured," he told media.

"The bomb had been planted by the enemies because this morning a coalition convoy was supposed to cross the area," he said, referring to NATO forces.

"Coalition forces helped us to evacuate the injured."

Civilian casualties in the war in Afghanistan are largely caused by Taliban attacks, according to surveys.

Roadside bombs are the Taliban`s main weapon in the war, now approaching the end of its ninth year.