In remarks at the start of the weekly cabinet meeting, Prime MinisterBenjamin 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.

“Whoever wants me as a strong prime minister cannot have a strong prime minister while weakening me,” Mr. Netanyahu told Israel Radio in an interview broadcast Sunday. “I think there is only one way to guarantee that the right continues to govern Israel, and that is to vote for me.”

Political polls in recent weeks have consistently shown that Likud-Beiteinu is bleeding votes to the Jewish Home, a far-right party led by Naftalie Bennett, a dynamic newcomer to national politics who is a former Netanyahu aide, settler leader and technology entrepreneur. Mr. Netanyahu also warned of possible efforts by centrist and leftist parties to create a united bloc aimed at thwarting his chances of forming the next coalition government.

Last week, in a pre-election move intended to highlight one of his government’s achievements, the prime minister toured the new security fence that runs almost the entire length of Israel’s border with Egypt. Accompanied by a group of Israeli journalists, Mr. Netanyahu noted that the barrier had sharply stemmed the flow of African migrants into Israel and had provided more protection against militant groups operating in the Sinai Peninsula in Egypt.

Mr. Netanyahu has pledged to erect a similar barrier along the Syrian frontier, with changes to suit the topography. A section of an old and rickety border fence near the Golan Druse village of Majdal Shams has already been fortified with a steel barrier after protesters, most of them Palestinians, breached the frontier in 2011, drawing deadly fire from Israeli soldiers.

Israel seized a large portion of the Golan Heights, a strategic plateau that overlooks northern Israel, from Syria in the 1967 war and later annexed it in a move that has not been internationally recognized. The cease-fire line was established in the aftermath of the 1973 conflict, and though Israel and Syria are still technically at war, it has remained mostly quiet for decades.

Israel has largely stayed out of the fighting in Syria, but in recent months a number of stray Syrian mortar shells crashed into the Israeli-controlled territory as Syrian government forces battled rebels across the line. As a result, Israel fired warning shots into Syria and in one instance aimed tank fire at a Syrian artillery position.

Apprehension has been mounting, with Israeli experts warning that Syria is becoming a haven for Islamic extremists. Israel says that thousands of Islamic militants have entered Syria to fight against forces loyal to President Bashar al-Assad, and Israeli leaders have expressed particular concern that chemical weapons and advanced weaponry like ground-to-air missiles amassed by the Assad government could fall into the hands of radical groups.

As a result, Israel has been changing its military infrastructure along the frontier with Syria, planning a continuous fence and the installation of electro-optical devices and radar, and deploying some of its most highly trained troops there for the first time in more than 30 years.