The Isis affiliate in Egypt is staging increasingly sophisticated and daring attacks, officials and analysts say, prompting Israel, Egypt and the Palestinian militant group Hamas to form an unlikely alliance against the terrorist group.
Hamas deployed several hundred fighters last week to Gaza's border with Egypt's lawless northern Sinai as part of a deal with Egypt to keep militants of Isis (Islamic State) from entering the coastal enclave.
That came days after Israeli Prime Minister Benjamin Netanyahu praised his country's decision to build a new barrier along the Israel-Egypt border, warning that "we would have been overflowed by thousands of Isis fighters from Sinai".
The growing concerns have given birth to the greatest co-operation between the militaries of Egypt and Israel since their 1979 peace deal, according to officials from both countries.
The question is whether the militants' ambitions can be stopped or, at least, contained.
The well-armed affiliate - known as Wilayat Sinai - has grown bolder since it asserted responsibility for the October bombing of a Russian charter flight over the Sinai Peninsula, killing all 224 aboard. The group has mounted a steady stream of attacks on Egyptian soldiers, over-running military posts and targeting them with roadside bombs.
In the April issue of an Isis newsletter, al-Naba, the terror group boasts about the attacks.
Egyptian intelligence bodies have struggled to penetrate the sanctums of the secretive militants, said Israeli military officials and Egyptian activists and residents in the Sinai.
"They have genius strategists," said Mohannad Sabry, an Egyptian journalist and author of a book on the Islamist insurgency in the Sinai. "If you study the map of their attacks, they obviously know what they are doing exactly, and it shows they have a great deal of freedom of mobility."
Last weekend, General Joseph Dunford, chairman of the US Joint Chiefs of Staff, made his second trip to Egypt in two months to discuss the Sinai and regional security.
The US and Israel are particularly concerned that the militants could threaten a multinational peacekeeping effort that has overseen the peace between Egypt and Israel along the Sinai border. Some member countries providing troops could be targeted for taking part in the broader operations.
A Hamas official last week said there are now more than 300 Hamas fighters deployed in three areas along the sea and two land border crossings with the Sinai.
- Washington Post, Bloomberg