BAGHDAD (Reuters) – Iraqi Shi’ite militiamen machine gunned minority Sunni Muslims in a village mosque on Friday, killing dozens just as Baghdad is trying to build a cross-community government to fight Sunni militants whose rise has alarmed Western powers.

A morgue official in Diyala province north of Baghdad said 68 people had been killed in the sectarian attack staged on the Muslim day of prayer. Ambulances took the bodies 60 km (40 miles) to the provincial capital of Baquba, where Iranian-trained Shi’ite militias are powerful and act with impunity.

Attacks on mosques are acutely sensitive and have in the past unleashed a deadly series of revenge killings and counter attacks in Iraq, where violence has returned to the levels of 2006-2007, the peak of a sectarian civil war.

Lawmaker Nahida al-Dayani, who is from Diyala, said about 150 worshippers were at Imam Wais mosque when the militiamen arrived following a roadside bombing which had targeted a security vehicle. “It is a new massacre,” said Dayani, a Sunni originally from the village where the attack happened.

“Sectarian militias entered and opened fire at worshippers. Most mosques have no security,” she told Reuters. “Some of the victims were from one family. Some women who rushed to see the fate of their relatives at the mosque were killed.”

The bloodbath marks a setback for Prime Minister-designate Haider al-Abadi, from the majority Shi’ite community, who is seeking support from Sunnis and ethnic Kurds to take on the Islamic State insurgency that is threatening to tear Iraq apart.

An army major who declined to be named said the gunmen arrived in two pickup trucks after two bombs had gone off at the house of a Shi’ite militia leader, killing three of his men.

A Sunni tribal leader, Salman al-Jibouri, said his community was prepared to respond in kind. “Sunni tribes have been alerted to avenge the killings,” he said.

In the northern city of Mosul, Islamic State stoned a man to death, witnesses said, as the United States raised the prospect of tackling jihadist safe havens across the border in Syria.

In a regional conflict which is throwing up dilemmas for governments from Washington to London to Baghdad and Tehran, any U.S. action against Islamic State in Syria would risk making common cause with President Bashar al-Assad – the man it has wanted overthrown in a three-year uprising.