A bomb explosion ripped through the Rawda mosque roughly 40 kilometres west of the North Sinai capital of El-Arish before gunmen opened fire.
Masked gunmen attacked a bus carrying Coptic Christians on a visit to a monastery south of the Egyptian capital on Friday.
The attacks in the Nile Delta cities of Tanta and Alexandria followed a Cairo church bombing in December.
Egypt is enraged after footage showed 21 handcuffed hostages in orange jumpsuits being beheaded by black-suited captors on a beach.
A coalition has called for a boycott of Egypt’s vote for a new constitution, which some see as an "indictor" of the army chief’s presidential bid.
Ex-president Hosni Mubarak’s release has added new elements to Egypt’s political turbulence as members of the Muslim Brotherhood are rounded up.
Egypt’s hardline military leader has warned against further protests in the country as the EU prepares to hold talks on the crisis.
At least 74 supporters of Egypt’s ousted Islamist president have been shot dead during clashes with security forces, officials said.
Tens of thousands of Islamists poured onto Egypt’s streets demanding ousted president Mohamed Morsi be put back in power.
Egypt’s new prime minister has gotten closer to forming a cabinet as supporters of Mohamed Morsi vow to keep fighting for his reinstatement.