Gunmen have shot dead a prominent Sunni Arab tribal chief, his three sons and a son-in-law as they slept in their home in Baghdad, police say.
Dozens have gone to Khadim Hemaiyim's home to mourn
Khadim Sarhid al-Hemaiyim was the leader of the al-Batta tribe, a branch of the al-Dulaym tribe, one of the largest Sunni tribes in Iraq.
Officials said gunmen dressed in Iraqi army uniforms broke into his house and opened fire with automatic weapons.
The killings are the latest in a series of attacks on Sunni Arab leaders.
The gunmen arrived at the house in Baghdad's south-eastern al-Hurriya district at 0400 (0100 GMT) in 10 armoured cars similar to those used by Iraqi security services.
"I saw it with my own eyes. They were soldiers," Mr Hemaiyim's son, Thair Khadim Sarhid, told Reuters.
Mr Sarhid said that he and two of his dead brothers were policemen.
"I am going to get rid of my police badge. From now on I will be a terrorist," he said.
Sunni leaders have frequently accused Shia militias within the Iraqi security apparatus of operating death squads with a sectarian agenda.
A spokesman for the Iraqi military said that its forces were not involved in the killing and that it was likely to have been militants in disguise.
"Surely, they are outlaw insurgents. As for the military uniform, they can be bought from many shops in Baghdad," Maj Falah al-Mohammedawi said.
"Also, we have several police and army vehicles stolen and they can be used in the raids."
Mr Hemaiyim's brother said that his family had been attacked before.
"His eldest son was assassinated one month ago in the Taji area of northern Baghdad, when unidentified men shot and killed him," he said.
Dozens of people went to Mr Hemaiyim's home to mourn the five men.
Correspondents says the attack is likely to increase tensions between Sunni and Shia Arabs in the capital, which are already running high in the run-up to December's parliamentary elections.
It also comes a week after US troops found 173 mostly Sunni Arab prisoners - some of whom had reportedly been tortured - in a bunker in an Iraqi interior ministry building.
In a separate incident, the former chief of the traffic police in Baghdad was killed in Baghdad.
Gen Mahdi Kassim was shot by gunmen in his home in the Yarmouk district in south-west Baghdad, police said.
A senior official in the industry ministry, Radi Ismail Jawad, was also shot and killed near his home in west Baghdad.