Vast areas of Egypt’s Sinai desert have descended into lawlessness in recent months, providing fertile ground for small cells of extremist militants that have emerged from the shadows and quietly established training camps near the Israeli border, according to Bedouin elders and security experts.

The militants include men who have fought in Afghanistan and Pakistan in recent years, as well as Islamists who were released from prison after the 2011 popular revolt that toppled President Hosni Mubarak and drove much of his potent security apparatus underground.