Egyptian police said they found the decapitated head in Sinai on Friday of a man kidnapped by Islamist militants, reportedly for his role in assassinating an extremist.
A security official said another man, also accused in the assassination, was believed to have been kidnapped by the Bedouin militants.
A Bedouin tribal source said the head, found in the Muqatta area in North Sinai, belonged to Manazil Bereikat from the same tribe of an extremist killed in a mysterious explosion near the Israeli border on 26 August.
At the time, witnesses had said the militant, Ibrahim Ouda Bereikat, died in a blast as he tried to fire a rocket into Israel. Security sources said he might have been killed by a landmine.
The Bedouin source, who requested anonymity because of the sensitivity of the subject, said the militants behind Manazil's kidnapping accused him and several other men of planting a booby trap to assassinate Ouda Bereikat.
The security official said two other men the militants were hunting to avenge Ouda Bereikat's death fled across the border into Israel.
The Egyptian military and police have bolstered their presence in the lawless peninsula to battle Islamist militants after gunmen killed 16 soldiers at a border outpost on 5 August.
The military on Wednesday said it has killed 11 militants and arrested 23 since the start of an unprecedented campaign involving tanks and helicopters.
