KABUL, Afghanistan -- A man in an Afghan military uniform killed three U.S. troops Friday in southern Afghanistan, a day after the United States condemned a suicide bomb attack that left four Americans dead.
The man opened fire on the troops in the volatile Helmand province, said Maj. Lori Hodge, a spokeswoman for the International Assistance Security Force.
It is the latest in a series of so-called "green on blue" attacks that has seen attackers dressed in Afghan security force uniforms turn their weapons on NATO soldiers.
Hodge did not immediately provide details about the attack, one of a handful of attacks in recent weeks to target NATO troops.
In a separate incident on Friday, a NATO soldier was killed in an insurgent attack in southern Afghanistan, officials said. Details of the attack, including the location, were not released, however officials said the soldier was not an American.
The developments came a day after Secretary of State Hillary Clinton condemned an attack in the eastern Kunar province "that killed USAID Foreign Service Officer Ragaei Abdelfattah, three ISAF service members and an Afghan civilian, and injured a State Department Foreign Service officer."
"On behalf of President Obama and the American people, I have sent my deepest condolences to Ragaei's family and to the entire U.S. Mission in Afghanistan," Clinton said in a written statement released late Thursday.
The Department of Defense released few details about the attack that occurred Wednesday, saying only that the three American troops died "of wounds suffered when they encountered an insurgent who detonated a suicide vest."
The Taliban claimed responsibility for the attack, saying two bombers targeted the American soldier near the entrance of the compound of the province council in Asadabad, according to a statement released by spokesman Zabiullah Mujahid.
The Taliban claimed to have killed 17 soldiers, though the group is known to routinely claim responsibility for attacks and inflate casualty numbers.
Mujahid said the attack occurred as the troops were exiting a military vehicle and gathering to enter the compound.
Killed in the explosion was Army Command Sgt. Maj. Kevin J. Griffith, the senior enlisted soldier of the 4th Brigade Combat Team, 4th Infantry Division from Fort Carson, Colorado, the Department of Defense said.
Also killed were Army Maj. Thomas E. Kennedy, 35, of West Point, New York, and Air Force Maj. Walter D. Gray, 38, of Conyers, Georgia, the Defense Department said.
Troops were also wounded in the attack, said Major Martyn Crighton, a spokesman for the NATO-led International Security Assistance Force Joint Command.
Crighton would not release the number of injured but said "all the seriously wounded were evacuated to Germany."
The attack is the latest in a series of high profile strikes against NATO and Afghan officials, and it comes as the United States is reducing its troop strength ahead of an anticipated 2014 hand over of responsibility to Afghan forces.
Kennedy served on the brigade staff, while Gray was a flight commander attached as a liaison to the brigade, according to their respective service records.
Griffith, 45, of Laramie, Colorado, was the brigade's senior ranking non-commissioned officer, the Defense Department said.
Griffith, who joined the Army in 1988, participated in the U.S.-led invasion of Iraq in 2003, according to his service records. He deployed twice more to Iraq, once in 2007 and again in 2009.
He deployed to Afghanistan in March with a headquarters company of the brigade.
Kennedy was commissioned as an officer in 2000. He served two tours in Iraq in 2003 and 2005.
According to his service record Kennedy deployed to Afghanistan on July 18.
Gray was assigned to the 13th Air Support Operations Squadron at Fort Carson.
An Afghan interpreter was also killed, the State Department said.
CNN's Ben Brumfield, Samuel Gardner III and Greg Morrison contributed to this report. Carter reported from Atlanta and Popalzai from Kabul.