As the Iraqi government bolstered Baghdad’s defences on Sunday, the Islamic militant group that captured two major cities last week posted graphic photos that appeared to show its fighters massacring dozens of captured Iraqi soldiers.

The pictures on a militant website appear to show masked fighters of the Islamic State of Iraq and the Levant, or ISIL, loading the captives onto flatbed trucks before forcing them to lie face-down in a shallow ditch with their arms tied behind their backs. The final images show the bodies of the captives soaked in blood after being shot.

The grisly images could further sharpen sectarian tensions as hundreds of Shiites heed a call from their most revered spiritual leader to take up arms against the Sunni militants who have swept across the north. ISIL has vowed to take the battle to Baghdad and cities further south housing revered Shiite shrines.

A car bomb meanwhile exploded in central Baghdad, killing 10 and wounding 21, according to police and hospital officials. Baghdad has seen an escalation in suicide and car bombings in recent months, mostly targeting Shiite neighbourhoods or security forces.

While the city of seven million is not in any immediate danger of falling into the hands of the militants, Sunday’s bombing could raise tensions. Food prices in the city have risen, twofold in some cases, because of disruption to transport on the main road heading north from the capital.

The government bolstered defences around Baghdad on Sunday, a day after hundreds of Shiite men paraded through the streets with arms in response to a call by Grand Ayatollah Ali al-Sistani for Iraqis to defend their country. ISIL has vowed to attack Baghdad but its advance to the south seems to have stalled in recent days. Thousands of Shiites have also volunteered to join the fight against the ISIL, also in response to al-Sistani’s call.

Armed police, including SWAT teams, were seen over the weekend manning checkpoints in Baghdad, searching vehicles and checking drivers’ documents. Security was particularly tightened on the northern and western approaches of the city, the likely targets of any advance by ISIL fighters on the capital. The city looked gloomy on Sunday, with thin traffic and few shoppers in commercial areas.

At one popular park along the Tigris river, only a fraction of the thousands who usually head there were present on Sunday evening. In the commercial Karada district in central Baghdad, many of the sidewalk hawkers who sell anything from shoes to toys and clothes were absent.

In Baghdad, Iraqi government officials said ISIL fighters were trying to capture the city of Tal Afar in northern Iraq on Sunday and raining down rockets seized last week from military arms depots. The officials said the local garrison suffered heavy casualties and the town’s main hospital was unable to cope with the number of wounded, without providing exact numbers.

Iraq’s top military spokesman, Lt. Gen. Qassim al—Moussawi, confirmed that fighting was raging at Tal Afar, but indicated that the militants were suffering heavy casualties. On all fronts north of the capital, he said, a total of 297 militants have been killed in the past 24 hours.

ISIL and allied Sunni militants captured a vast swath of northern Iraq last week, including second city Mosul and Saddam Hussein’s hometown of Tikrit, as Iraqi troops, many of them armed and trained by the U.S., fled in disarray, surrendering vehicles, weapons and ammunition to the powerful extremist group, which also fights in Syria.

The captions of the photos say the killings were to avenge the killing of an ISIL commander, Abdul—Rahman al—Beilawy, whose death was reported by both the government and ISIL shortly before the al—Qaida splinter group’s lightning offensive, which has plunged Iraq into its bloodiest crisis since the withdrawal of U.S. troops in 2011.

“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.

Al—Moussawi, the military spokesman, confirmed the photos’ authenticity and said he was aware of cases of mass murder of captured Iraqi soldiers in areas held by ISIL.

More In: World | International | News