KABUL, Afghanistan — NATO said Saturday it was continuing its inquiry into the Oct. 3 bombing of a Doctors Without Borders hospital in northern Afghanistan and had appointed three U.S. military officers from outside the chain of command to handle the investigation to ensure impartiality.

Gen. John Campbell, the commander of NATO's Resolute Support Mission which is training Afghanistan's security forces, has appointed U.S. Army Maj. Gen. William Hickman and two brigadier generals to continue the investigation begun by Brig. Gen. Richard Kim, NATO said in a statement.

"We will be forthright and transparent and we will hold ourselves accountable for any mistakes made," the statement quoted Campbell as saying. "While we desire the investigation to be timely, what's most important is that it be done thoroughly and correctly."

U.S. gunships bombed the Doctors Without Borders hospital in the city of Kunduz on Oct. 3, killing at least 13 staff members and 10 patients. Many were wounded. The main building was destroyed and the hospital has been shut down.

The international medical charity, which is also known by its French acronym MSF, said Friday it is trying to determine the identities of seven bodies found in the wreckage which were unrecognizable and have since been buried.

President Obama has apologized for the attack, which happened as Afghan forces battled Taliban insurgents who had stormed Kunduz on Sept. 28 and briefly held the city of 300,000, the first provincial capital they have overrun since being forced from power in late 2001.