Gunmen in Egypt's restive Sinai peninsula, a hotbed of Islamist militant activity, killed three policemen on Monday and gunned down a civilian in a separate attack, security officials said.

Masked attackers shot three policemen guarding a police station in the North Sinai town of El-Arish before fleeing, an official said.

In the Sheikh Zuwayed area, near the border with the Gaza Strip, unidentified gunmen opened fire near a checkpoint, killing a civilian, another official said.

Militants in Sinai intensified their campaign against security forces after the military ouster of Islamist president Mohamed Morsi on July 3.

Dozens of soldiers and policemen have been killed in daily attacks, as the army has poured troops and armour into the lawless peninsula that straddles Africa and Asia to crush the insurgency.

The offensive in Sinai comes as part of a massive crackdown by the army-installed authorities on Islamists, which has seen hundreds killed and more than 2,000 arrested nationwide.

Morsi, the country's first democratically elected leader, is himself detained, as is the leadership of his Muslim Brotherhood.

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