Sinai-based militant group Ansar Bayt Al-Maqdis has claimed responsibility for Tuesday's assassination of an aide to the interior minister.
Meanwhile, an army spokesperson blamed the attack on the Muslim Brotherhood.
Early on Tuesday two assailants on a motorcycle shot dead General Mohamed Said, head of the minister’s technical office, while he was leaving his home in Giza's Haram district.
Ansar Bayt Al-Maqdis, an ideological offshoot of Al-Qaeda, which has claimed responsibility for multiple attacks in Egypt since July 2013, also threatened to kill Interior Minister Mohamed Ibrahim, Defence Minister Abdel-Fattah El-Sisi and their aides, Al-Ahram Arabic news website reported.
In a statement on his official Facebook account, army spokesperson Ahmed Ali denounced a separate attack on a church in 6 October City on Tuesday afternoon that left one dead, for which he also blamed the Brotherhood.
Egypt has witnessed a surge in attacks by Islamist militants in Cairo, the Nile Delta and the Sinai Peninsula.
Four bombs exploded in Cairo the day before the third anniversary of the January 25 revolution, including one at the capital's main police headquarters. The blast killed six people and damaged the nearby Islamic Museum.
The interior minister survived an assassination attempt in September.
Ansar Bayt Al-Maqdis has claimed responsibility for most of the recent attacks.
The Muslim Brotherhood was labelled a terrorist organisation in late December 2013.