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

The United States launched dozens of against ISIS targets in central Syria on Sunday in an attempt to "disrupt, degrade and defeat" the terrorist group, according to the head of the U.S. Central Command.

CENTCOM Commander Gen. Michael Erik Kurilla said in a statement that 75 ISIS targets were hit in precision airstrikes Sunday in Syria. He said the mission was carried out by U.S. Air Force assets, including B-52s, F-15s and A-10s.

"There should be no doubt -- we will not allow ISIS to reconstitute and take advantage of the current situation in Syria. All organizations in Syria should know that we will hold them accountable if they partner with or support ISIS in any way," Kurilla said.

Kurilla said the strikes hit known ISIS camps and operatives in central Syria.

During a speech at the White House on Sunday, President Joe Biden mentioned the U.S. strikes on ISIS targets in Syria. He said U.S. forces are also bolstering security at detention facilities in Syria where ISIS fighters are being held.

"We're clear-eyed about the fact that ISIS will try to take advantage of any vacuum to reestablish its capability and to create a safe haven," Biden said. "We will not let that happen."

-ABC News' Cindy Smith