Israel has been alerting Western and Arab nations to the growing coordination between Hamas in the Gaza Strip and ISIS-affiliated groups in the Sinai Peninsula, a researcher with the Washington Institute for Near East Policy wrote on Tuesday.

While the intelligence-sharing was met with skepticism at first — Israel was reluctant to share its sources — the growing body of evidence has apparently led to a widespread reassessment among diplomatic and intelligence agencies, wrote Ehud Yaari, Israeli Channel 2‘s Arab affairs analyst.

Egypt, Yaari wrote, is convinced Hamas is aiming to undermine security in the Sinai even as it negotiates improving ties with Cairo — a relationship which soured after the Egyptian army deposed former Islamist president Mohamed Morsi and launched a sustained crackdown on the Muslim Brotherhood.

The Egyptian army has also been battling armed terrorists in the Sinai, including locally recruited Bedouins, who carry out almost daily attacks against security outposts, road blocks and administrative facilities.

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These terrorist groups, including ISIS Sinai Province — an organization previously under a different name and affiliated with al-Qaeda — are primarily coordinating with Hamas officials to move weapons through the vast Sinai Peninsula, for a substantial cut, according to Yaari. For political cover, Hamas leaders have avoided direct contact with members of these groups, relying instead on members of their military branch to do the legwork.

“This cooperation culminated in a prolonged secret visit to Gaza this month by IS Sinai’s military chief Shadi al-Menai, who held talks with his counterparts in Hamas’s military wing, the Izzadin al-Qassam Brigades (IDQB),” wrote Yaari. “Menai has been at the top of Egypt’s most wanted list since an attempt to kill him failed in May 2014.”

On Wednesday, Israeli media reported that Egyptian aircraft used Israeli air space to carry out airstrikes against ISIS in Sinai. Israel relaxed certain conditions in its peace accords with Egypt several years ago to allow the Egyptian military to deploy and patrol near the Israeli and Gazan borders.