Israel has claimed that Hamas is aiding ISIS's branch in Egypt's Sinai Peninsula in order to free up arms-smuggling routes into Gaza, in preparation for its next war with Israel.
In an interview with Israel Radio, a senior IDF officer responsible for monitoring Israel's southern borders with Gaza and Egypt claimed that, despite the ideological differences between them, a strategic alliance has been forged between Hamas in Gaza and ISIS's "Sinai Province."
"Why was it is so very important for them [Hamas] to develop the connection with Sinai Province? Because they need the raw materials that would enable the military build-up in Gaza," the Israeli colonel said, according to Reuters.
"To carry out high-quality smuggling required a special operation," he added, speaking on the eve of the one-year anniversary of Operation Protective Edge, and on condition of anonymity.
Hamas is banking on the success of "Sinai Province" in driving the Egyptian military from parts of Sinai - particularly those bordering Gaza - with the "objective of opening up a conduit" into Gaza, he said.
Under the rule of current President Abdul Fatah al-Sisi, Egypt has taken a hard line against Hamas - the Palestinian branch of the Muslim Brotherhood - systematically destroying its vast network of smuggling tunnels from Sinai into Gaza, and even imposing a "buffer zone" between Egypt and Gaza.
Together with Israel's own limited blockade of the Hamas-ruled enclave, those measures have made it difficult for Hamas to rebuild its badly-damaged capabilities and infrastructure, in particular its stockpile of heavy weapons and advanced, medium- and long-range rockets.
Hamas for its part has repeatedly rejected claims by Israel that it is aiding ISIS, which is also gaining a foothold in Gaza itself. Israeli officials have accused Hamas of playing an active part in the recent deadly assault on Egyptian forces in Sinai which left some 100 people dead.
But Hamas leaders have in turn accused Israel of "sending ISIS" to overthrow Hamas's rule in Gaza, following clashes between pro-ISIS elements and Hamas authorities.
But those clashes are notably local in nature, and have only involved Salafi-jihadist factions "inspired by" or loosely affiliated with ISIS - as opposed to "Sinai Province," which is ISIS's only official branch in the region.
Hamas official Sami Abu-Zuhri accused Israel of conducting "a systematic incitement campaign" via the claims.
"The Egyptian side understands that Hamas had no connection to what happened in Sinai and also realizes the efforts Hamas is making to to keep Gaza away from what happens there," he said.
It would not be the first time Hamas has cooperated with a groups or states with whom it is at odds with ideologically. The Sunni Islamist terror group has for years received support from Shia Islamist Iran and its main proxy Hezbollah.
That assessment is also shared by Israeli Defense Minister Moshe Yaalon.
Speaking Tuesday, he drew a distinction between the local conflict between Hamas and ISIS sympathizers in Gaza, and cooperation between Hamas and "Sinai Province" in Egypt.
"Hamas is fighting ISIS in the Strip, but on the other side there is cooperation between Hamas elements from Gaza and ISIS in Sinai," Yaalon stated.