* Men abducted by gunmen two days ago
* Sisi has said militants pose regional, global threat
* Sinai-based militants have attacked on Egypt mainland
CAIRO, Aug 20 (Reuters) - Four beheaded corpses were found by residents of a town in Egypt's Sinai Peninsula on Wednesday, security sources said, blaming Islamist militants waging an insurgency against Cairo.
The security sources in Sinai and Cairo, said residents of Sheikh Zuwaid found the bodies two days after the men were abducted by gunmen while travelling in a car in the town, a few kilometres from the Gaza Strip.
Though the men were civilians, they may have been targeted for their perceived allegiance to the police and army, the sources said, speaking on condition of anonymity. They gave no other indication of the identity of the men.
The militants have stepped up attacks on policemen and soldiers since then-army chief Abdel Fattah al-Sisi toppled President Mohamed Mursi of the Muslim Brotherhood in July 2013.
The government does not distinguish between the Sinai militants and the Brotherhood, which it has designated a terrorist group although the movement says it is peaceful and denies any links to the wave of militant attacks.
Sisi, now elected president, said last month that Islamist militants were ravaging the Middle East and pose a threat to security globally.
The Sinai militants are not believed to be officially linked to Islamic State insurgents who have swept through parts of Iraq and Syria and have releaesd a video purporting to show the beheading of a U.S. journalist.
The attacks by the Egyptian militants initially targeted security forces in Sinai - a remote but strategic part of Egypt located between Israel, the Gaza Strip and the Suez Canal - but they have since extended their reach to the mainland with bombings of security installations.
The government says nearly 500 people, mostly from the army and police, have been killed in clashes and in attacks by Islamist insurgents angered at Mursi's removal. Rights groups have put the number far higher, saying that many hundreds of Brotherhood supporters, meanwhile, have been killed at the hands of security forces.
A security crackdown since Mursi was ousted has also seen many thousands of Islamists arrested. More than 1,000 have been sentenced to death. Secular liberals accusing the government of rights abuses have also been jailed.
Seventeen pro-Brotherhood protesters were sentenced to life in prison by an Egyptian court on Wednesday on charges including murder and possession of arms during clashes that erupted at a protest in August 2013.
Rights groups say trials of Islamists have generally violated the most basic rights of citizens to fair hearings due to a lack of evidence against the defendants, among other problems.
(Reporting by Yusri Mohamed in Ismailia and Mahmoud Mourad in Cairo; Writing by Maggie Fick; Editing by Alison Williams)
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