U.S. military officials say they have identified the four Marines seen on video urinating on the bodies of dead Afghan Taliban fighters.
The Naval Criminal Investigative Service, heading the main inquiry into the video, has also reportedly questioned two of the men.
The four were members of a 1,000-man battalion from Camp LeJeune, North Carolina. Two of the men had moved onto other assignments before the video appeared on the Internet.
Officials say the men were members of a sniper unit in the 3rd Battalion, 2nd Marines. The group was deployed in the southern Afghan province of Helmand for seven months before returning home in September of last year.
Top U.S. officials, including Defense Secretary Leon Panetta and Secretary of State Hillary Clinton, have condemned the video, Panetta calling it "utterly deplorable."
On Friday, the commander of the International Security Assistance Force in Afghanistan expressed his outrage over the video.
General John Allen, currently traveling in the United States, said such acts must be condemned in the "strongest manner possible." He also said those responsible would be held accountable.
Several officials say that if the incident is confirmed, the Marines involved could be charged with war crimes for not treating the bodies of those killed in war honorably.
The video appears to show Marines in combat uniforms urinating on three corpses. In the footage, one person suspected of committing the act says "have a nice day," referring to one of the dead.
U.S. Defense Secretary Leon Panetta spoke by phone Thursday with Afghan President Hamid Karzai and affirmed there will be a serious probe into the incident.
Mr. Karzai said his government is "deeply disturbed" by the video, calling the act "simply inhuman."
A Taliban spokesman said while the video is "shocking," he did not think it would derail peace talks with the United States.
The commandant of the U.S. Marine Corps said he has requested the Marines and U.S. Navy conduct separate investigations into the video. He said the Marine Corps remains committed to upholding the Geneva Convention, the laws of war and its own core values.
Some information for this report was provided by AP and AFP.