BAGHDAD — Iraqi Shi’a militia forces executed 15 alleged Islamic State militants and then hung them from electricity poles in a public square in the town of Baquba, northeast of Baghdad, on Wednesday, police said.

With Iraq sliding ever closer to all-out sectarian civil war, a car bomb exploded near restaurants and shops in the capital’s Shi’a district of Sadr City, killing 16 people, while another car bomb killed five in Baghdad’s Ameen district, police said.

A police officer at the scene in Baquba, a mixed Sunni and Shi’a town 65 km (40 miles) from Baghdad, said he believed the gruesome display of the bodies was designed to warn Sunnis off supporting the Islamic State.

The victims, who had been kidnapped over the last week, were shot in the head and chest and then hung up by cables.

“The militia forces are preventing the medical crew from taking down the bodies,” the police officer said.

“They are following a new tactic of keeping bodies hanging for a longer time to deter the Sunni population from backing the Islamic State. We asked them to let us evacuate the bodies but they refused.”

The U.S.-funded and trained Iraqi army unraveled in the face of the Islamic State’s sweep through the north, and violence in other parts of Iraq has increased since then, raising fears that the OPEC member will relapse into the dark days of sectarian civil war that peaked in 2006-2007.

On the battlefield, Shi’a militias have stepped in to challenge the Sunni insurgents after Iraq’s top cleric called on his compatriots to take up arms against the Islamic State.

The United States plans to sell 5,000 Hellfire missiles to Iraq in a $700 million deal, officials said Tuesday, in what would be the largest sale of lethal weapons to Iraq.