An Iraqi tribal leader has been killed in a suicide bombing at his house south-east of Baquba, police say.
There have been a number of female suicide bombers in Diyala
Thaer Ghadban al-Karkhi was the head of one of the majority-Sunni Arab Awakening Councils, allied with the US military against al-Qaeda in Iraq.
A woman detonated an explosives vest after he answered the door, killing him, his niece and two guards.
Sunni militias have been credited with helping to bring down the level of violence in Iraq in recent months.
However, its members have frequently been targeted for attack by al-Qaeda militants.
The head of the Awakening Council in Anbar, Sheikh Abdul Sattar Abu Risha, a key US ally who was widely credited with having defeated al-Qaeda in much of western Iraq, was assassinated in September.
Correspondents say female suicide bombers have been involved in at least 19 attacks or attempted attacks since the anti-US insurgency began in 2003.
The BBC's Hugh Sykes in Baghdad says the increased use of female suicide bombers may be evidence of tighter security, because men are more likely to be searched thoroughly.
Diyala province - where Monday's attack occurred - has recently been the focus of such attacks by female suicide bombers.
Two other bombings in Iraq have been reported.
In another part of Diyala, a bomber blew himself up at the gate of a police station, killing two people, police said.
Twenty people, two of them policemen, were also wounded in the attack.
And in Baghdad, police said one person was killed and five wounded when a bomb in a parked minibus exploded in the northern Shaab district.