An insurgent group named the Islamic State of Iraq announced on Monday that it had executed two US soldiers who went missing last month. If confirmed, this act would constitute a serious violation of international humanitarian law and those responsible would be guilty of war crimes, Human Rights Watch said today.

On Monday, television networks around the world showed a video clip purportedly made by the Islamic State of Iraq, which showed what appears to be both the missing soldiers’ identification cards. In the video, the insurgent group, which in the past has claimed links to al-Qaeda, claims that it executed the men.

“Those claiming to hold the US soldiers captive must treat the men humanely,” said Sarah Leah Whitson, Middle East director at Human Rights Watch. “If they have done otherwise, they have committed war crimes.”

The two soldiers – Specialist Alex Jimenez, 25, and Private Byron Fouty, 19 – went missing on May 12 when insurgents ambushed their patrol near the town of Mahmoudiya, 30 kilometers (20 miles) south of Baghdad. In the Euphrates River, US forces later found the body of Private First Class Joseph Anzack, Jr., a third US soldier who went missing at the same time.

US forces subsequently deployed some 4,000 troops, backed by Iraqi army soldiers, to sweep through a large swath of territory around Mahmoudiya in search of the missing soldiers. In a statement, the US command said that American troops had detained 11 people and questioned 450 in connection with the search.

On May 14, two days after the soldiers went missing, the Islamic State of Iraq issued a statement calling on both US troops and the Iraqi Army to halt their search if they wanted their soldiers back alive. In the video clip that aired on Monday, the insurgent group stated that it had killed the US soldiers because US troops and the Iraqi army had failed to heed its warnings.

“Fearing the occupying army will continue its searches, harming our Muslim brothers, we decided to settle the matter and announced the news of their killing to cause bitterness to God’s enemies,” a spokesman for the Islamic State of Iraq said in the video.

Customary international law requires that all captured belligerents be treated humanely and provides that the murder or willful killing of a captured belligerent is a war crime.

“No matter what the cause, killing captives violates international humanitarian law,” said Whitson. “Every party to a conflict is subject to the laws of war, and the requirement to treat captive soldiers humanely is one of the most basic provisions.”

Executing a captured combatant also violates basic precepts of Islamic law governing the conduct of war, according to most scholars of Islamic law.

Human Rights Watch has documented violations of the laws of war of all parties to the conflict, including insurgent groups, US forces and the Iraqi government forces.