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.

It’s not certain whether the dead were Taliban fighters, civilians or someone else.

The incident will likely 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.

It also comes at a delicate time in relations among the United States, Afghanistan’s elected government and the Taliban insurgency fighting for both territorial control and cultural and religious preeminence in Afghanistan. The U.S. is trying to foster peace talks between the Karzai government and the Pakistan-based Taliban high command, and has made unprecedented offers to build trust with the insurgents, including the planned opening of a Taliban political office to oversee talks.

Anti-American sentiment is already on the rise in Afghanistan, especially among Afghans who have not seen improvements to their daily lives despite billions of dollars in international aid. They also have deplored the accidental killing of civilians during NATO airstrikes and argue that foreign troops have culturally offended the Afghan people, mostly when it comes to activities involving women and the Quran, the Muslim holy book.

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.

Karzai called the video “completely inhumane.” The Afghan Defense Ministry called it “shocking.” And the Taliban issued a statement accusing U.S. forces of committing numerous “indignities” against the Afghan people.