Sunni militants in Iraq have posted photos showing an alleged massacre of captured soldiers. The government has meanwhile bolstered defenses around the capital, Baghdad.
The photos, posted on a militant website run by the Islamic State of Iraq and Syria (ISIS), appear to show the dead bodies of hundreds of captured Iraqi soldiers lying in a shallow ditch.
Captions on the photos say the killings were in revenge for the death of an ISIS commander, Abdul-Rahman al-Beilawy.
"This is the fate that awaits the Shiites sent by Nouri to fight the Sunnis," one caption read, apparently referring to Iraq's Shiite Prime Minister Nouri al-Maliki.
Last Friday, UN human rights chief Navi Pillay warned against "murder of all kinds" and other war crimes in Iraq, saying the number killed in recent days mihgt run into the hundreds.
US State Department spokeswoman Jen Psaki said the ISIS militants' claim of killing the Iraqi troops was "horrifying and a true depiction of the bloodlust that those terrorists represent."
The images could aggravate sectarian tensions in Iraq after hundreds of Shiite volunteers took up arms at the bidding of their spiritual leader, Grand Ayatollah Ali al-Sistani.
Early last week, Sunni ISIS fighters swept across the north, capturing the two major cities of Mosul and Tikrit last week.
Attack on Baghdad?
There have also been unconfirmed reports of major fighting around the city of Tal Afar in northern Iraq. Tal Afar is mainly inhabited by Turkmen, an ethnic minority.
ISIS has vowed to move on Baghdad, but its advance seems to have slowed in the past few days. The government has nonetheless bolstered defenses around the capital in preparation for a possible attack.
Despite the added security, Baghdad saw a string of deadly explosions on Sunday that killed at least 15 people, according to hospital and police officials.
The city has seen a recent increase in suicide and car bombings, most of them targeting Shiite neighborhoods or security forces.
Disruption to transport on the main road leading north from the capital had led to a steep increase in food prices.
The United States has ordered an aircraft carrier into the Gulf in response to the crisis, as President Barack Obama considers possible military options for Iraq.
tj/ipj (AP, dpa)