A bomb blast beside Egypt’s foreign ministry killed three policemen on Sunday, including a key witness in a trial of deposed Islamist President Mohammad Mursi.
The blast, the worst attack in Cairo for months, killed two police lieutenant colonels and a recruit, Reuters news agency quoted the foreign ministry.
Ajnad Misr, the Islamist militant group that carried out the last significant attack in Cairo, claimed responsibility for the blast in a statement posted on their official Twitter account.
"This new operation shows we can penetrate and reach the vicinity of the Ministry of Foreign Affairs...to destroy the officers of the criminal security agencies and make them taste some of what they have made Muslims taste," it said.
"Operations of retribution and revenge by this blessed group will not stop," said the group, whose name means Soldiers of Egypt.
One of the police officers killed in the blast, Lt. Col. Mohamed Mahmoud Abu Sareeaa, was a critical witness in a trial of Mursi related to a 2011 mass prison break, court and security sources told Reuters.
It was not clear if he was targeted or just happened to be at the site of the explosion
The blast was the latest attack in a simmering insurgency against the U.S.-backed government, underlining security challenges facing President Abdel Fattah al-Sisi.
State television earlier reported that the blast occured along a sidewalk in the neighborhood of Boulaq abu Eila, which houses the foreign ministry and state television headquarters beside the Nile.
Live television footage showed the aftermath of the blast, which brought a tree down on a nearby car. Policemen with sniffer dogs were scouring the area for more bombs.
Militants have killed scores of policemen in bombings and shootings since Egypt's military toppled Mursi in July 2013.
Militants have in the past set off several bombs in succession, to target first responders after the initial attack.
Attacks in the capital raise concerns over security forces, who have vowed to end Islamist militant bloodshed that has hammered the tourism industry, a pillar of the economy.