At least 20 people were killed Thursday in militant attacks on numerous army and police locations in Egypt's Sinai Peninsula, authorities said.
The attacks, which included mortar rounds fired at the headquarters of the security directorate in the provincial capital, El Arish, also injured dozens.
An army spokesman accused the Muslim Brotherhood of orchestrating the attacks.
The attacks included a car bomb set off outside a military base while mortar rounds were fired at the base, toppling some buildings and burying soldiers, officials said.
Other attacks included mortar rounds fired at a hotel, a police club and more than a dozen checkpoints, officials said.
The militants struck El Arish, the nearby town of Sheik Zuweid and the town of Rafah, which borders the Gaza Strip.
The spokesman said the attacks came in response to "successful strikes by the armed forces and police against terrorist elements and spots of late in North Sinai."
The Muslim Brotherhood is the group from which ousted Islamist President Mohamed Morsi hails. Along with allies, it has been staging protests for a year and a half against what it describes as a "military coup" in Egypt. Protesters often clash with security personnel.
Egypt's security apparatus has been combating an Islamist insurgency that has become rampant since Morsi's ouster in 2013.
Twenty-three people, including three policemen, died in nationwide clashes between dissidents and police forces Sunday, the fourth anniversary of the uprising that toppled longtime leader Hosni Mubarak. The deadliest violence Sunday took place in Cairo.