KABUL, Afghanistan (AP) — A roadside bomb killed six civilians and wounded more than a dozen others in southern Afghanistan, authorities said Sunday, hours after a suicide bomber killed four in an attack on a military bus in the capital.

The attack in the south happened when an improvised explosive device hit a taxi Sunday evening, said Omar Zwak, a spokesman for the governor of Helmand province. He added that 13 people were wounded.

Bombs in vehicles, along roadsides and carried by suicide bombers are the Taliban's weapons of choice and the leading cause of civilian casualties in Afghanistan. The United Nations has blamed insurgents for the overwhelming majority of such attacks, and said they have increased as the Taliban try to regain territory as foreign troops withdraw.

Earlier Sunday, a suicide bomber attacked a military bus in Kabul, killing at least four people — including two soldiers.

Gen. Mohammad Zahir Azimi, spokesman for the Defense Ministry, said the bomber waited on foot in the east of the city for the bus to arrive before setting off his explosives. He said the dead included two soldiers and two civilians, one of whom was a woman. He says 22 others were wounded.

Taliban spokesman Zabihullah Mujahid claimed responsibility for the attack in an email sent to media.