The brazen kidnapping and slaying of a Sunni sheik and eight members of his entourage in the Iraqi capital was met with outrage by Sunni politicians Saturday, deepening sectarian distrust and threatening to tear apart the country’s fragile government.

Sunni politicians said they would boycott parliament after the killing of Sheik Qasim al-Janabi, a moderate Sunni tribal leader, his son and the other members of their convoy, blaming the Friday night assault on Shiite militias that they say the government has allowed to act with impunity. Discussions continued into the night as to whether Sunni parties should pull out of the government altogether.

Such a move would strike a blow to the inclusive Iraqi government that Prime Minister Haider al-Abadi created under pressure from the United States, which had tied his efforts to reach out to Sunnis to military assistance.

While Iraqi and U.S. officials say that bringing in Iraq’s Sunnis and helping them fight the Islamic State is an essential part of defeating the group, Sunni politicians say they’ve heard promises but seen little action.

“The bullet that shot Sheik Qasim also shot at the heart of national reconciliation,” said Sunni parliamentarian Raad al-Dahlaki. “The government has nice words but doesn’t execute its promises. It’s too weak to control the militias.”

Mourners carry a coffin during the funeral of prominent Iraqi Sunni tribal leader Sheikh Qasim al-Janabi and his son, Mohammad, who were killed in an attack on their convoy, in Baghdad Saturday. (Stringer/Reuters)

Iraq’s Shiite militias have flourished since the Islamic State’s advance across the country last summer, when the government was forced to rely on them for security as Iraqi army divisions disintegrated.

Although many credit the ­Iranian-backed militias with saving the capital from falling, with their growth in strength have come accusations of mass killings and forced displacement of Sunnis.

While not the most grievous of such acts leveled at the country’s Shiite militias, the fact that the Janabi slaying occurred in central Baghdad drew particular ire.

The sheik and his group were pulled over at a fake checkpoint in the city’s southwest. Their bodies — hands bound and shot execution style — were later found dumped in a largely Shiite neighborhood in the city’s northeast. Janabi’s nephew, a member of parliament, was kidnapped with him but was released after being severely beaten.

The perpetrators wore the uniforms of Iraqi security forces, he told the local news media.

“This happened in the center of Baghdad, not the desert,” Iraq’s Sunni deputy prime minister, Saleh al-Mutlak, told Sharqia television from the sheik’s funeral. “They must have had to drive them through 50 checkpoints. Where are the security services? Where is the government? We are at the mercy of these gangs.”

A close friend of the slain tribal leader, Mutlak said Janabi had been a voice of moderation. His son, Mohammed al-Janabi, had just returned to the country after studying law at Glasgow University in Scotland.

“This is it,” Mutlak said. “We can’t stay in this miserable political process any longer. We can’t stay in a government while our sons are being slaughtered.”

Hakim al-Zamili, who heads parliament’s defense and security committee, promised that the incident would be investigated. But many Sunnis are skeptical.

Zamili is a militia leader accused of running death squads during Iraq’s sectarian war. The interior minister is a member of the Badr Brigades, another Shiite militia.

While Shiite militias are well-armed and funded, Sunni tribes that have been fighting the Islamic State complain that they are getting little support, stoking distrust further.

“This just helps Islamic State portray itself as the one who is looking after Sunnis,” said Dhafer al-Ani, a spokesman for the Sunni Mutahidoon party.

He gave as an example al-Baghdadi, a town in western Iraq that fell to the militants last week, threatening the nearby air base where more than 300 U.S. Marines are stationed. Sunni fighters there fought with little support for months before relenting, he said.

“They get nothing, but the Shiite militias get support from Iran and the government,” he said. “This all makes the level of trust very weak.”