Two international soldiers were shot dead in Afghanistan today, NATO said.

The nationality of the two victims was not officially announced, but military officials told CBS News that they were both American.

According to a NATO statement, two gunmen fired “indiscriminately” on International Security Assistance Force (ISAF) troops and Afghan security forces in southern Afghanistan. One attacker is “believed to be an Afghan National Army service member,” ISAF said. The other was wearing civilian clothes.

CBS reported that a third US soldier was injured in the attack. At least two of the gunmen were killed when ISAF troops returned fire; there are reports that a third shooter was also involved, and was wounded.

A district governor in Kandahar province said the attack took place at a joint ISAF-Afghan base in the village of Sangisar, the Los Angeles Times reported. Niaz Mohammad Sarhadi identified the shooter as a civilian employed by the Afghan military as a literacy tutor, who said he had snatched a weapon from an Afghan soldier.

Just hours before the shooting, according to the BBC, ISAF commander General John R. Allen described the recent violence in Afghanistan following the burning of Qurans at a NATO base as a “setback” that would be overcome. The network reported:

Gen. Allen said he would be willing to walk, unarmed, into the Afghan Interior Ministry in Kabul, where two NATO military advisers were shot dead last Saturday.

All NATO military advisers were withdrawn from Afghan ministries following that incident; today, some began returning to their posts, the New York Times reported. A NATO spokesman did not specify which ministries were involved.

According to the Times, three separate investigations are underway into the burning of Qurans at Bagram Air Base last week: one American, one Afghan, and one joint inquiry by Afghanistan and the US. Only the investigation by the US military will carry any formal legal weight, the newspaper said.

A joint NATO-Afghan inquiry is nearly complete, officials told the Associated Press, with preliminary findings expected to be published within the week. 

According to the AP:

A separate investigation by a group comprising representatives from the country’s council of Muslim clerics, members of parliament and government officials was delivered to President Hamid Karzai days after the incident. Karzai could release its findings as early as this weekend.

A total of six NATO personnel have been killed since protests began, at least four of them American. More than a dozen Afghan have died in the riots.