WASHINGTON -- Pentagon leaders scrambled Thursday to contain damage from an Internet video purporting to show four Marines urinating on Taliban corpses -- an act that appears to violate international laws of warfare and further strains U.S.-Afghan relations.

Defense Secretary Leon Panetta called Afghan President Hamid Karzai to offer assurances of a full investigation and the top Marine general promised an internal probe as well as a criminal one. Investigators moved quickly to identify and interview at least two of the four Marines. They were members of a battalion that fought for seven months in former Taliban strongholds in southern Afghanistan.

Their unit, the 3rd Battalion, 2nd Marines, returned from Helmand province to its home base at Camp Lejeune, N.C., last September. Marine officials said that a battalion officer confirmed to investigators on Thursday, based on his examination of the video, that the four men depicted urinating had been members of the battalion. Two have since moved on to other units.

As the video spread across the Internet in postings and re-postings, U.S. officials joined with Afghans in calling it shocking, deplorable, inhumane and a breach of military standards of conduct. It shows men in Marine combat gear standing in a semicircle urinating on the bodies of three men in standard Afghan clothing, one whose chest was covered in blood.

The incident likely will further hurt ties with Karzai's government and complicate negotiations over a strategic partnership arrangement meant to govern the presence of U.S. troops and advisers in Afghanistan after most international combat troops withdraw by the end of 2014.

Pentagon officials said the criminal investigation would likely look into whether the Marines violated laws of war, which include prohibitions against photographing or mishandling bodies and detainees. It also appeared to violate the U.S. Uniform Code of Military Justice, which governs conduct. Thus, some or all of the four Marines could face a military court-martial or other disciplinary action.

Asked how the development might affect U.S.-Afghan-Taliban peace efforts, Secretary of State Hillary Clinton did not directly reply. "The United States remains strongly committed to helping build a secure, peaceful, prosperous, democratic future for the people of Afghanistan," she said. "And we will continue to support efforts that will be Afghan-led and Afghan-owned to pursue the possibility of reconciliation and peace."