twelve soldiers belonging to Iran’s Revolutionary Guard Corps were killed in Sunday’s Israeli air strikes on Syria, the UK-based NGO Syrian Observatory for Human Rights claimed on Tuesday.

The report said a total of 21 people were killed in the strikes, among them six Syrian soldiers and 15 non-Syrian nationals, 12 of whom were IRGC soldiers, making it the deadliest attacks by Israel so far in the war-torn country.

Israel’s security cabinet will meet Wednesday to discuss the increased tensions in the North following the latest confrontation between the two enemy states, Ynet news reported on Tuesday.

The meeting will be the first for new IDF Chief of Staff Lt.-Gen. Aviv Kochavi.

Israel’s military made a rare admission of responsibility as it was carrying out the strikes, writing on Twitter at 1:42 a.m. that “We have started striking Iranian Quds targets in Syrian territory. We warn the Syrian Armed Forces against attempting to harm Israeli forces or territory.”

IDF fighter jets struck Iranian and Syrian military targets, air defense batteries and Quds Forces positions throughout Syria in the predawn hours of Monday, targeting military targets belonging to Iran’s Quds Force in Syria, including weapons storage sites, a site at Damascus International Airport, an Iranian intelligence site and an Iranian training camp.

The IDF said that jets struck several Syrian air defense batteries after dozens of anti-aircraft missiles were fired toward the Israeli jets despite the warning.

Israel’s military said the widespread air strikes came as a response to a surface-to-surface missile that was launched towards the Golan Heights by Iranian forces in the vicinity of the Syrian capital of Damascus.

The missile, reported to be carrying a half-ton warhead and aimed at deterring Israel from conducting further airstrikes in Syria, was intercepted by the Iron Dome missile defense system.

The IDF Spokesperson’s Unit also said in a statement that “the Iranian attack on Israeli territory yesterday is yet another clear proof of the intention behind the attempts to establish Iran in Syria and the danger they pose to the State of Israel and regional stability. The IDF will continue to act decisively and firmly against the Iranian establishment in Syria.”

Following the strikes, Syria’s SANA news agency reported that the Assad regime sent two identical letters to the UN Secretary General and the Head of the Security Council calling on them to take immediate steps to prevent further Israeli air strikes and to hold it accountable for “its crimes against the Syrian and Palestinian people.”

“This aggression attempts to raise the morale of the remaining terrorist hotbeds that are subservient to the Israeli occupation, in addition to being an attempt by the occupation authorities to avoid their escalating internal problems,” the report said, adding that “Syria affirms that Israel’s persistence in its dangerous aggressive behavior wouldn’t be possible without the unlimited support of the US administration and the immunity provided to it by the US and other Security Council member states.”