Armed militants killed at least 30 policemen in a shootout during a raid on a suspected militant hideout in Egypt's Western desert, security sources said on Friday.
A number of suspected militants were also killed and security forces are combing the area, a statement by the Interior Ministry said.
Egypt is facing an Islamist insurgency concentrated in the Sinai peninsula from two main groups, including an Islamic State affiliate, that has killed hundreds of security forces since 2013.
Islamist militants have launched several major attacks, most recently targeting churches in Cairo and other cities with the loss of dozens of lives.
The security sources said authorities were following a lead to a hideout deep in the desert thought to house eight suspected members of Hasm, a group which has claimed several attacks around the capital targeting judges and police since last year.
A convoy of four SUVs and one interior ministry vehicle was ambushed from higher ground by militants firing rocket-propelled grenades and detonating explosive devices, a senior source in the Giza Security Office said.
The number of dead was expected to rise, two security sources said.
Two security sources said eight security personnel were injured in the clashes, while another source said that four of the injured were police and four others suspected militants.
Egypt accuses Hasm of being the militant wing of the Muslim Brotherhood, an Islamist group it outlawed in 2013. The Muslim Brotherhood denies this.
The Islamist insurgency in the Sinai peninsula has grown since the military overthrew President Mohamed Mursi of the Muslim Brotherhood in mid-2013 following mass protests against his rule.
The militant group staging the insurgency pledged allegiance to Islamic State in 2014. It is blamed for the killing of hundreds of soldiers and policemen and has started to target other areas, including Egypt's Christian Copts.