According to Syrian media reports, Israeli warplanes have carried out dozens of attacks across the country, including on the capital Damascus.
The Britain-based Syrian Observatory for Human Rights (SOHR) said more than 100 attacks on military targets had taken place.
According to local media reports, a research center with suspected links to chemical weapons production was among the sites hit.
Israel says it is taking action to prevent weapons from falling “into the hands of extremists” after the overthrow of the Assad regime.
Meanwhile, the UN Security Council is meeting to discuss the situation in the country following the fall of President Bashar al-Assad.
The SOHR says hundreds of Israeli airstrikes have taken place over the past two days, including on a site in Damascus reportedly used by Iranian scientists for missile development.
The attacks come as the UN chemical watchdog warns authorities in Syria to ensure suspected stockpiles of chemical weapons are safe.
According to the UN chemical watchdog, the Organization for the Prohibition of Chemical Weapons (OPCW), a chemical weapon is a chemical used to deliberately cause death or damage through its toxic external properties.
The use of chemical weapons is prohibited under international humanitarian law regardless of the presence of a valid military target, as the effects of such weapons are indiscriminate by nature.
It is not known where and how many chemical weapons Syria has, but former President Bashar al-Assad is said to have stockpiled and that the statement he made was incomplete.
Syria signed the OPCW chemical weapons certificate in 2013, a month after a chemical weapons attack on the outskirts of the capital Damascus involving the nerve agent sarin and killing more than 1,400 people.
The gruesome images of victims convulsing in pain shocked the world. Western powers said the attack could only be carried out by the government, but Assad blamed the opposition.
Despite the OPCW and UN destroying all 1,300 tons of chemicals declared by the Syrian government, chemical weapons attacks continued in the country.
Analyzes by the BBC in 2018 confirmed that chemical weapons were used at least 106 times in the Syrian civil war between 2014 and 2018.
On Monday, the OPCW said it had contacted Syria “to emphasize the paramount importance of ensuring the safety and security of all chemical weapons-related materials and facilities” in the country.
Also on Monday, the Israeli military released photos of its troops moving from the Israeli-occupied Golan Heights into the demilitarized buffer zone in Syria where U.N. peacekeepers are stationed.
It comes a day after Israeli Prime Minister Benjamin Netanyahu announced that the military had temporarily taken control of the so-called Area of Separation, saying the 1974 withdrawal deal with Syria had “collapsed” due to the country’s takeover rebels.
The Golan Heights is a rocky plateau about 60 kilometers southwest of Damascus.
Israel captured the Golan from Syria in the closing stages of the 1967 Six-Day War and unilaterally annexed it in 1981. This move was not internationally recognized, although the US did so unilaterally in 2019.
Saar said at a press conference on Monday that the Israeli Defense Forces (IDF) were only taking “a very limited and temporary step” taken for “security reasons.”
He also claimed that Israel had no interest in interfering in internal Syrian affairs and was only concerned with defending its citizens.
Defense Minister Israel Katz, meanwhile, said the Israeli army would “destroy heavy strategic weapons” – including missile and air defense systems.
Israel’s latest moves come after Syrian rebel fighters captured the capital Damascus and overthrew Bashar al-Assad’s regime. He and his father had been in power in the country since 1971.
Forces led by the Islamist opposition group Hayat Tahrir al-Sham (HTS) entered Damascus in the early hours of Sunday, before appearing on state television to declare that Syria was now “free”.
On Sunday, Netanyahu called the collapse of the Assad regime a “historic day in the Middle East.”
The Assad regime received significant support from Hezbollah and Russia in the country’s brutal civil war. With Hezbollah involved in the war between Israel and Gaza and in cross-border airstrikes between Israel and Lebanon, and Russia dedicating enormous resources to its invasion of Ukraine, HTS, together with other rebel groups in Syria, was able to seize this opportunity and ultimately be able to carry out major conquer parts of Syria.
During the 2011 Syrian uprising, Israel made the calculation that Assad, despite being an ally of both Iran and Hezbollah, was a better bet than what his regime might follow.
On Sunday, Netanyahu insisted that Israel would “send a hand of peace” to Syrians who wanted to live in peace with Israel.
He said the IDF presence in the buffer zone was a “temporary defensive position until a suitable arrangement is found.”
“If we can establish neighborly and peaceful relations with the new forces emerging in Syria, that is our wish. But if we don’t, we will do whatever it takes to defend the State of Israel and Israel’s border,” he said.
Israel is likely to be more sensitive towards the Golan Heights as the family of HTS leader Abu Mohammed al-Jawlani has roots there. Thousands of Israeli settlers now live in the area, along with about 20,000 Syrians, most of whom are Druze, who stayed after the area was conquered.
Israeli attacks in Syria are nothing new. It has previously acknowledged carrying out hundreds of attacks in recent years on targets in Syria that it says are linked to Iran and allied armed groups such as Hezbollah.
Israeli attacks in Syria have reportedly become more frequent since the start of the war in Gaza in October 2023, in response to cross-border attacks on northern Israel by Hezbollah and other groups in Lebanon and Syria.
Just last month, the Syrian Observatory for Human Rights (SOHR), a British monitoring group, reported that a series of attacks hit an arms depot and other locations in and around an area near Palmyra where families of Iranian-backed militia fighters were located. killing 68 Syrian and foreign fighters.