Updated

A homicide bomber rammed his explosives-laden car into a minibus full of Afghan soldiers south of Kabul on Wednesday, killing at least 13 people and wounding 20, officials and witnesses said.

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

Gen. Mohammad Zahir Azimi, a defense ministry spokesman, said six soldiers and seven civilians were killed in the attack. Four of the civilians were children, said Abdullah Fahim, a health ministry spokesman.

The homicide bomber 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.

Purported Taliban spokesman Zabiullah Mujaheed claimed responsibility for the blast in a text message sent to an Associated Press reporter in neighboring Pakistan.

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

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

Local resident Amir Mohammad said he helped load the bodies of the six slain Afghan soldiers into ambulances.

Mohammad Amin, who runs a bakery close to 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 defense ministry," Amin said. "Suddenly today a very strong explosion hit the bus."

At least 13 civilians were wounded in the attack, according to Fahim, the health ministry spokesman.

Mohammad Ashraf, 13, was praying inside a mosque when the flying shrapnel and glass cut through his flesh, his father Mohammad Akram said.

"My other 8-year-old son was also wounded in the same mosque," Akram said.

There has been a spate of attacks in recent months on buses carrying Afghan security forces as they commute to work in the morning.

On Sept. 29, a bomber blew himself up inside an army bus in Kabul, killing 28 soldiers and two civilians. In June, another bomb ripped through a bus carrying police instructors in Kabul, killing 35 people.

Militants have launched more than 133 attacks this year — a record number. At least 6,200 people have died in insurgency-related violence in 2007, also a record, according to an Associated Press tally of figures from Afghan and Western officials.

Bomb attacks frequently target international and Afghan security forces, but most of the casualties are civilian passers-by.

In southern Afghanistan, U.S.-led coalition troops killed several Taliban militants during raids on compounds in Garmser district on Wednesday, the coalition said in a statement.

The troops "targeted an individual believed to be associated with weapons smuggling operations in the province," it said. "While performing a search of one of the compounds, coalition forces killed several armed militants who posed an imminent threat."

Separately, an explosion struck a patrol of NATO-led troops in southern Afghanistan on Tuesday, leaving one soldier dead and two others wounded, the alliance said in a statement.