A classified cable sent to Israeli ambassadors by Israel’s Foreign Ministry warned that Syrian dictator Bashar Assad may again utilize chemical weapons in an ongoing civil war, and such chemicals may spill over into Israel, according to Israel’s Channel 10 news.

The cable warned that Israel would react with severity against Syria if chemical weapons were used anywhere near the Israeli border.

“It must be made clear that such an incident would require Israel to respond in the strongest possible terms,” the cable stated. “We must convey the message that Israel will not allow this and will defend itself, its citizens and its sovereignty.”

Ambassadors were asked to inform senior political leaders in the countries where they’re stationed of the threat of an escalation of hostilities if Iran is continued to be allowed to entrench in Syria. The cable also encouraged ambassadors to call for international pressure on Iran to halt aggression towards Israel and ongoing support for Hezbollah.

The ministry sent the warning to 15 Israeli ambassadors around the world as part of guidelines issued on addressing the topics of Iran, Syria and the Hezbollah terror organization in their host countries, following a military escalation this week between Israel and Syria.

Syrian anti-aircraft missiles downed an Israeli F16 after Israel shot down an Iranian drone that penetrated Israeli airspace, and then retaliated on numerous military installations in Syria, including the drone’s launch site. After the F16 was hit, Israel launched another set of reprisals that reportedly neutralized up to half of Syria’s air-defense capabilities.

Though Syria’s government denied owning chemical weapons, calling them “immoral and unacceptable,” a joint investigation team of experts from the United Nations and the Organization for the Prohibition of Chemical Weapons concluded that Assad used Sarin nerve gas in an aerial attack on Khan Sheikhoun that killed 100 people in April, and used chlorine gas in at least two attacks on his opponents in 2014 and 2015.