A recently-emerged militant group called the Hasm Movement has claimed responsibility for a car bomb attack in Cairo that killed six policemen.
The organisation, which has claimed several attacks in Egypt in recent months, made the announcement in an internet posting on Friday.
Six policemen were killed and three wounded when a roadside bomb exploded near a security checkpoint in Cairo. Four civilians were hurt.
The attack, close to a government building in a middle class neighbourhood of Cairo, was the latest in a series of security incidents in Egypt often claimed by radical Islamists.
The policemen were either in or near their car when the device went off, the sources said.
The interior ministry said a security cordon had been thrown around the scene of the attack near a mosque in the Giza district of the Egyptian capital.
Eyewitness Ahmed Al-Deeb described a scene of carnage, with dead and dying policemen lying next to wrecked cars.
One of the policemen had blast fragments in his chest and two more had lost legs, he told Reuters Television.
Security forces killed three gunmen on Tuesday in a raid on a hideout in southern Egypt used by what they described as an armed wing of the Muslim Brotherhood, which claimed responsibility in September for an assassination attempt on a senior prosecutor.
An Egyptian general was killed by militants on November 4 near his home in North Sinai in an attack for which Islamic State claimed responsibility.
He was the second military officer of his rank to be shot dead in as many weeks.
Hundreds of soldiers and police have been killed in an Islamist insurgency led by Islamic State in the Sinai Peninsula.
Attacks have stepped up since the military overthrew President Mohamed Mursi of the Muslim Brotherhood, Egypt's oldest Islamist movement, in 2013 following mass protests against him.
Judges, policemen and senior officials have been targeted by radical Islamists angered by long prison sentences imposed on members of the now-outlawed Brotherhood.