Syria's Assad is now in Moscow, Russian state media says

Israeli Foreign Minister Gideon Saar told reporters on Monday that Israeli forces "attacked strategic weapons arrays, residual chemical weapons capabilities, missiles and long-range rockets" inside Syria to prevent them from falling into the hands of "extremist elements."

Israeli forces have been striking inside Syria and occupying positions on Syrian territory in recent days, as rebel forces -- some with roots in jihadist organizations -- surged into major Syrian cities and precipitated the collapse of President Bashar Assad's regime in Damascus.

The Israel Defense Forces announced on Sunday it had taken up positions in the demilitarized buffer zone between Israel and Syria established by a bilateral 1974 agreement.

Saar said the presence of "armed men" in the zone and their alleged attacks on United Nations positions there prompted the Israeli decision to cross the border.

Saar said Israeli deployments into the buffer zone are "targeted and temporary" and intended to prevent an "Oct. 7 scenario from Syria," referring to last year's devastating Hamas infiltration attack into southern Israel.

-ABC News' Jordana Miller and Dana Savir

Israel Defense Forces tanks and armored vehicles have entered the buffer zone that separates the Israeli-occupied Golan Heights from Syria on Sunday night.

The move puts IDF troops in operations on four fronts in the Middle East, Israeli military chief of staff Herzi Halevi said on Sunday, according to the Associated Press.

The advancement into Syria comes after the fall of President Bashar al-Assad's regime to Islamist rebels.

Israeli Prime Minister Benjamin Netanyahu said the decision was made to "protect Israeli residents after Syrian troops abandoned positions," according to AP.

The IDF has reportedly warned Syrian residents in five southern communities to stay home for their safety.

Israeli forces on Sunday also took over the Syrian side of Mount Hermon in the Golan Heights, according to AP.

The Syrian Civil Defence, known as the White Helmets, said on Sunday that it sent “five specialized emergency teams” to Sednaya prison “to search for secret cellars inside the prison where detainees are expected to be present,” in a post on X.

"The teams include a search and rescue team, a team to dig through walls, a team to open iron doors, a team of trained dogs, and an ambulance team," the post said.

Sednaya prison, operated by ousted president Bashar al-Assad’s government, is known colloquially as the “human slaughterhouse.” It is located near Damascus.

-ABC News' Ellie Kaufman

Iranian Foreign Minister Abbas Araghchi commented on the fall of Syria's government during an interview on Iranian state TV on Sunday.

He said Syria's ousted president, Bashar al-Assad, was “surprised” and “complained about the way his own army was performing.”

Araghchi also said Iran was fully aware of the situation in Syria through “the intelligence and security system of our country.”

Iran is monitoring the developments in Syria and is concerned about the “possibility of a renewed civil war or a sectarian war between different sects or the division of Syria and the collapse of Syria and its transformation into a haven for terrorists,” Araghchi said.

-ABC News' Hami Hamedi and Ellie Kaufman