An Afghan police officer retrieves documents stained with blood after a car bomb in Kandahar. The attack killed at least seven people and wounded 19 on Sunday. (Ahmad Nadeem/Reuters)

At least five Afghan police officers and two civilians were killed Sunday when a car bomb was detonated outside the main police headquarters in Kandahar, officials said.

An additional 19 people, six of them police officers, were wounded in the blast, provincial officials said. Children also were among the victims.

No group has claimed responsibility for the attack, but a spokesman for the governor blamed Taliban insurgents.

The southern Afghan city has been the scene of such attacks before, as violence grows in many parts of the country despite an influx of foreign troops.

In a separate incident, Afghan officials announced Sunday that a U.S. soldier fatally shot an Afghan guard Friday night at a U.S. base in northern Afghanistan.

The guard was on duty at the gate of a base in Sar-e Pol when the incident occurred. Provincial governor Sayed Anwar Rahmati said the U.S. soldier opened a door and saw the barrel of the guard’s gun. Feeling threatened, he fired.

“It was a mistaken act and happened due to the threat the soldier had felt from the guard,” Rahmati said by phone.

A spokesman for the NATO-led troops in Kabul said the coalition was aware of the report, but he would not provide further details, saying an investigation was underway.

According to reports, a dozen foreign troops have been killed recently, some of them by rogue Afghan forces at joint operating bases.

In the worst incident in recent months, four unarmed French troops were killed by an Afghan soldier northeast of Kabul. The incident followed a similar attack a few weeks prior against French troops by a man wearing an Afghan army uniform.

After the deaths, French officials announced that the country plans to withdraw its combat troops from Afghanistan by 2013, earlier than scheduled.

Some of the attacks have been blamed on personal, cultural and religious disputes, while others have been in retaliation for civilian casualties during foreign operations.

Taliban-led insurgents have also taken credit for some of the attacks, infiltrating the ranks of Afghan forces as they take on a greater security role in preparation for the withdrawal of international troops.

The attacks have caused distrust among international forces serving on joint duty or providing training for Afghan forces.

Salahuddin is a special correspondent.