In a joint statement Saturday, Secretary of State Hillary Clinton and Defense Secretary Leon Panetta offered their condolences for the loss of life and support NATO's immediate investigation.
Earlier Saturday, Pakistan demanded that the U.S. vacate a suspected drone base within 15 days, the Associated Press reports. The demand comes as the Pakistani government is claiming a NATO attack.
The base, Shamsi Air Base, is located in southwestern Baluchistan province.
Pakistan also closed both border crossings with Afghanistan, effectively halting the path of NATO supply trucks into the country.
In a statement, the White House expressed condolences, as well as "our desire to work together to determine what took place, and our commitment to the U.S.-Pakistan partnership which advances our shared interests, including fighting terrorism in the region."
Details of the attack are still sketchy, but the Pakistan government is saying that the attacks were unprovoked, a sentiment that wasn't dispelled by an unnamed Western diplomat who spoke to CBS News. "We don't know the full details yet," the diplomat said. "But it's possible the attack may have mistakenly targeted Pakistani soldiers on the assumption that they were militants."
NATO has said that they are investigating the incident which occurred just before dawn. Insurgents based across the Pakistan border are responsible for much of the violence in Afghanistan, but NATO forces are not allowed to cross over to attack them.
Regardless of how events unfolded, the incident will only further strain already fraught relations between Pakistan and Western forces. "How can anyone expect a regime in Islamabad to be giving more support to the U.S. when our soldiers are being killed in cold blood?" a senior Pakistan foreign ministry official asked CBS News.
The attacks come nearly a year after two Pakistani were killed after being mistaken for insurgents by a U.S. helicopter.