KABUL, Afghanistan -- A suicide bomber rammed his explosives-laden car into a minibus carrying Afghan soldiers south of Kabul on Wednesday, killing at least 13 people and wounding 20 others, officials said.

Meanwhile, Afghan forces clashed with Taliban who had blocked a main highway in the south, killing 10 militants, an official said.

The Kabul blast happened on the last day of Defense Secretary Robert Gates' two-day visit to Afghanistan, but it was not immediately clear if he was still in the country at the time. The Taliban claimed responsibility for the attack.

The suicide bomber's car struck a minibus full of soldiers in the Chihulsutoon area south of Kabul, said Aziz Ahmad, an Afghan army officer at the site of the blast.

Six soldiers and seven civilians were killed in the attack, and seven other soldiers were wounded, said Gen. Mohammad Zahir Azimi, a Defense Ministry spokesman.

At least 13 civilians also were wounded in the attack, said Abdullah Fahim, a spokesman for the Health Ministry. Four children were among those killed, Fahim said.

Purported Taliban spokesman Zabiullah Mujaheed claimed responsibility for the blast in a text message sent to an Associated Press reporter in neighboring Pakistan. Mujaheed identified the bomber as Abdul Rahman, from eastern Khost province.

The mangled frame of the minibus lay on the side of the road as the wounded were whisked to hospitals.

The blast was third suicide attack in the city in the last eight days. It followed a similar attack Tuesday against a NATO convoy that wounded 22 civilians.

Mohammad Amin, who runs a bakery near the blast site, said two of his employees were wounded by flying glass.

"Every day, this bus stops in front of my bakery to take employees of the Defense Ministry," Amin said. "Suddenly today, a very strong explosion hit the bus."