CAIRO - A bomb blast just beside Egypt's foreign ministry killed three policemen on Sunday, authorities said, in the most serious attack in Cairo in almost three months.
There was no immediate claim of responsibility for the bombing, which killed two police lieutenant colonels and a recruit, according to the foreign ministry.
But the operation resembled ones carried out by Islamist insurgents seeking to topple the U.S.-backed government, underlining security challenges facing President Abdel Fattah al-Sisi, who has just completed 100 days in office.
Sisi has pushed through some badly-needed economic reforms such as a rise in fuel prices. But tackling Islamist militants -- an issue that has dogged one Egyptian leader after another -- is far from easy.
Egypt has faced rising Islamist militant violence since Sisi deposed President Mohamed Morsi last year after mass protests against his rule and cracked down on his Muslim Brotherhood movement.
The challenge has become more complex since Islamic State militants seized parts of Iraq and Syria in June and declared a caliphate, inspiring other militant groups including some based along Egypt's border with chaotic Libya.
Islamic State established ties with Sinai-based Ansar Bayt al-Maqdis and has been coaching Egypt's most lethal militant organization, security officials and an Ansar commanders have stated.