NATO has confirmed that Afghan civilians died in a recent air strike on two stolen fuel tankers and a Canadian general will now lead an investigation into the deadly incident.

The air strike happened in the early hours of Friday, when German forces called in an attack on a pair of hijacked fuel tankers in the northern province of Kunduz. They believed that no civilians were present when the air strike was called in. But local officials have said dozens of civilians died in the ensuing explosion when the tankers were hit.

Both German and U.S. forces were involved in the strike on the fuel tankers.

On Tuesday, the NATO-led force in Afghanistan said that while commanders initially believed that only Taliban insurgents were in the area, a subsequent review has shown that "civilians also were killed and injured in the strike."

The NATO announcement about the fatalities came on the same day that an international convoy was attacked near the entrance to the military airport in Kabul. At least three civilians were killed in the blast caused by a Taliban car bomber, Afghan officials said.

Later in the day, the U.S. military announced that four American troops were killed in what a spokesperson described as a "complex attack" in Kunar province in eastern Afghanistan. No further details were provided.

U.S. Gen. Stanley McChrystal, the top U.S. and NATO commander in Afghanistan, has appointed Canadian Maj. Gen. C.S. "Duff" Sullivan to lead a joint investigation board that will probe the Kunduz air strike.

The board will also include a U.S. Air Force officer, a German officer and a legal advisor. Board members will co-ordinate with a separate Afghan investigation team that was put together by Afghan President Hamid Karzai.

The board is expected to take several weeks to complete its investigation. It will document its research thoroughly, while sharing information with Afghan and German authorities.

German Chancellor Angela Merkel said her government won't accept "premature judgments" about the deadly air strike, though she said "we will not gloss over anything" when the investigation results are released.

In Afghanistan, Sullivan serves as the Air Component Element Director and the Deputy of Joint Operations for the International Security Assistance Force.

Sullivan, a 30-year Canadian Forces veteran, previously helped investigate the friendly fire incident that took the life of Canadian Pte. Mark Anthony Graham three years ago.

In that incident, a U.S. Air Force plane mistakenly opened fire on Canadian troops during Operation Medusa near Kandahar. Four other soldiers were injured and Graham was killed.

With files from The Associated Press and The Canadian Press