Afghan civilians were killed and wounded in an airstrike by international forces targeting a Taliban commander in the volatile southern province of Helmand, NATO said Saturday, giving no details of numbers.

It said the International Security Assistance Force (ISAF) called in an airstrike on two vehicles believed to be carrying a Taliban leader and his associates, but later discovered they were transporting civilians.

"Afghan civilians were accidentally killed and wounded in Naw Zad district, Helmand province yesterday (Friday)," ISAF said in a statement, adding that it had launched an investigation into the incident.

Civilian casualties in military operations are highly sensitive in Afghanistan as coalition troops battle to curb a Taliban-led insurgency ahead of a planned handover of security to Afghan forces.

The latest incident came after nine people -- who Afghan officials said were children collecting firewood -- were killed in a NATO airstrike in eastern Kunar province, near the border with Pakistan, earlier this month.

The Kunar strike unleashed public fury over civilian casualties at a crucial time for foreign forces in Afghanistan, leading the US troop commander in Afghanistan, General David Petraeus, to issue a rare public apology.

Western-backed Afghan President Hamid Karzai, who has shaky relations with Washington, condemned those deaths and said Petraeus's apology was "not enough".

"The civilian casualties are a main cause of worsening the relationship between Afghanistan and the US," a statement from the Afghan presidency at the time quoted Karzai as saying. "The people are tired of these things and apologies and condemnations are not healing any pain."

Karzai argues that civilian deaths in NATO operations turn people against his pro-US administration and help the Taliban to recruit more fighters.

The United Nations says Afghan civilian deaths in the war increased 15 percent to a record high of 2,777 last year. More than three-quarters of the dead were killed in violence blamed on insurgents.

The number of civilian casualties linked to international military operations actually fell by 21 percent, but public anger surrounding the issue has grown as the conflict drags on.

Helmand, the heartland of the global opium trade, is one of the biggest flashpoints in the 10-year Taliban insurgency that erupted after a US-led invasion brought down their regime in 2001.

On Tuesday Karzai announced that the provincial capital, Lashkar Gah, would be among the first areas to be handed over to Afghan security forces in a transition process designed to allow foreign troops to leave by late 2014.

Officials in Helmand, where mobile phone networks have been cut off for several days on Taliban orders, could not immediately be reached for comment on the latest civilian casualties.