MOUNT HAZEKA, Israel — Elite infantry and reconnaissance units have been moved into the long-quiet Golan Heights this spring. Bulldozers are making way for new military shelters. And at an Israeli Army outpost on a strategic hilltop here, a Merkava tank sits pointing toward Syria — poised to race up a dirt ramp at a moment’s notice.

The stepped-up military presence across the 43-mile border demonstrates the growing fear and anxiety among Israeli leaders over the Syrian civil war. Already there have been clashes at the border, with errant munitions landing in the Golan some 30 times, at least five prompting Israel to fire back.

An Obama administration official said Friday night that Israeli aircraft bombed a target in Syria overnight on Thursday, and United States officials said they were considering military options, including carrying out their own airstrikes.

But the concern in Israel runs deeper along what was for decades one border it did not have to worry much about. Many increasingly see no possible positive outcome of their neighbor’s bloody conflict, no clear solution for securing their interests in the meanwhile. Israel’s military leadership now views southern Syria as an “ungoverned area” that poses imminent danger.