A Coptic Christian man was found decapitated on Thursday in Egypt's Sinai peninsula five days after he was kidnappped by gunmen, security officials and witnesses told AFP.

The man was found with his hands and feet bound and his head severed in the Sheikh Zuwayed area of north Sinai, they said.

A security official said "extremist groups" had captured the man on Saturday, the same day that a Coptic priest was killed.

Analysts had highlighted the danger of extremists exploiting tensions and unrest across Egypt since the military overthrew Islamist president Mohamed Morsi last week.

The Sinai has been plagued by security problems since early 2011 when president Hosni Mubarak was ousted.

Hardcore Islamist militants have used the sparsely populated north of the peninsula as a launching pad for attacks on security forces.