Civilian deaths by coalition forces have angered Afghan President Hamid Karzai  [Reuters]

A number of civilians have been killed and wounded in southern Afghanistan following a NATO air raid targeting two vehicles that coalition forces believed to be carrying Taliban fighters.

In a statement on Saturday, the coalition said that it was investigating the incident, but did not release the number of dead and wounded.

Nato said the International Security Assistance Force (ISAF) had called in an air attack on the two vehicles believing them to be carrying a Taliban leader and his associates, but later discovered they were transporting civilians.

The attack occurred on Friday in the Naw Zad district of Helmand province.

Civilian casualties in military operations in Afghanistan have become increasingly embarrassing for international forces battling the Taliban there ahead of a planned handover of security to Afghan forces.

The latest incident comes only two days after the coalition killed two civilians in the eastern province of Khost.

The two were walking near a car with suspected insurgents and were not seen until after a NATO helicopter gunship launched its attack, NATO said.

Civilian casualties

Earlier in the month, nine civilians, who Afghan officials say were children collecting firewood, were killed in a NATO air raid in eastern Kunar province, near the border with Pakistan.

The Kunar attack led to a rare public apology by General David Petraeus, the leading US troop commander in Afghanistan.

Hamid Karzai, Afghanistan's president, dismissed the apology as "not enough".

A recent UN report has said that at least 2,777 civilians were killed in fighting in Afghanistan in 2010.

Also on Saturday, Thomas de Maiziere, Germany's defence minister, visited Afghanistan in what was his first trip to there since taking taking the post.

German legislators have endorsed sending up to 300 crew members to man surveillance planes in Afghanistan, a move intended to take pressure off NATO allies enforcing a no-fly zone over Libya.

De Maiziere and Abdul Rahim Wardak, his Afghan counterpart, discussed Kabul's recent announcement that Afghan security forces would take the lead in seven areas across the nation from July.