Gunmen shot dead eight policemen Sunday in a Cairo suburb, the latest in a series of assaults targeting security forces in Egypt.
The plainclothes officers were inside a small bus in the southern suburb of Helwan when the gunmen came out of a pickup truck, opened fire and then fled, the Interior Ministry said in a statement.
The attack was carried out by four assailants using automatic rifles, the ministry added.
Pictures carried by Egyptian media showed the police microbus riddled with bullets and stained with blood.
There were conflicting claims of responsibility for the ambush.
A local group loyal to the Islamic State extremist militia said it was behind the killings.
In an online statement circulated by its supporters, the group Islamic State in Egypt alleged the attack had been mounted by its members and that the gunmen seized weapons from the slain officers before fleeing the scene unharmed.
The group said that the assault was in "revenge" for female prisoners in Egypt.
The statement could not be independently verified.
Islamic State has claimed responsibility for several of the deadly attacks that have targeted Egyptian security troops in the past two years.
Another group, calling itself Popular Resistance, said on Facebook that it carried out Sunday's attack in order to commemorate the 1,000th day after a deadly security crackdown on a Cairo protest camp by backers of the ousted president Mohammed Morsi of the Muslim Brotherhood.
Local media said that the Popular Resistance is a militant group linked to the now-banned Muslim Brotherhood.
There was no comment either from Egyptian authorities or the Muslim Brotherhood.
Egypt has seen a spate of attacks since the army's 2013 overthrow of Morsi following massive protests against his rule.