JERUSALEM — Israel announced Sunday that it was constructing a border fence along the length of its armistice line with Syria in the Golan Heights and that it was coordinating its intelligence with the United States in light of the deteriorating security situation in Syria.

In remarks at the start of the weekly cabinet meeting, Prime Minister Benjamin Netanyahu said that the Syrian Army had moved away from the frontier and that jihadist forces had moved in.

“Therefore, we will defend this border against both infiltration and terrorism,” Mr. Netanyahu said, adding, “I also submit to the cabinet the fact that the Syrian regime is very unstable, that the question of chemical weapons here worries us.” He said that Israel was coordinating with the United States and others “so that we might be prepared for any scenario and possibility that could arise.”

Mr. Netanyahu’s announcement came as he sought to reinforce his security credentials as a strong leader ahead of national elections on Jan. 22, and as he appealed to his traditional supporters to cast their ballots for the conservative Likud-Beiteinu ticket he is leading and not be lulled by polls showing that he is favored to win.