Israel Under Threat From Islamist State and Its New Allies

[From article]
This switch means that Israel, the U.S.’s closes ally in the Middle East, could be threatened from the southwest by the Egyptian ISIS group of Ansar Bait al-Maqdis in Sinai and by ISIS in southern Syria.
[. . .]
“If Israel was attacked by ISIS, America would expect a proportionate response by Israel, which is militarily capable of defending itself,” said Geoffrey Levin, a professor at New York University. “America would counsel against sustained Israeli involvement because it could threaten the tacit alliance between America, Iran, Turkey, and several Arab states against ISIS.”
[. . .]
Al-Yarmuk Martyrs Brigade controlled an area near the Jordan-Israel border in March 2013. That same month, the brigade took as hostages some of the United Nations peacekeeping mission soldiers. Even so, Israel reportedly allowed the brigade to have its wounded fighters treated in Israeli hospitals.

http://www.thefiscaltimes.com/2014/12/23/ISIS-Closing-Israel-North-and-South

ISIS Closing in on Israel from the North and the South
BY RIYADH MOHAMMED,
The Fiscal Times
December 23, 2014