Israeli Prime Minister Benjamin Netanyahu and Russian President Vladimir Putin sought to defuse a crisis on Tuesday after Syrian defences mistakenly downed a Russian warplane after Israeli air strikes.

The incident late Monday was the deadliest known case of friendly fire between Syria and its key backer Russia since Moscow’s game-changing 2015 military intervention.

Putin said it was the result of “tragic accidental circumstances”.

Syria is to blame for downing of plane, Netanyahu tells Putin

The Ilyushin plane dropped off the radar over the Mediterranean after Turkey and Russia announced a deal that offered millions of people reprieve from a threatened military assault in northern Syria’s Idlib province.

The deadly chain of events started when Israeli missiles struck the coastal region of Latakia.

Israel said it had targeted a Syrian military facility where weapons manufacturing systems were “about to be transferred on behalf of Iran” to Lebanese Shia group Hezbollah.

It sees Iran’s military presence in Syria as a threat, and Netanyahu told Putin by phone on Tuesday his forces would keep acting against it.

“Israel is determined to stop Iranian military entrenchment in Syria, and the attempts by Iran, which calls for the destruction of Israel, to transfer to Hezbollah lethal weaponry (to be used) against Israel,” said Netanyahu.

Israel expressed ‘sorrow’ for the Russian deaths, but insisted the Russian plane had been felled by “extensive and inaccurate Syrian anti-aircraft (surface-to-air missile) fire”.

Putin said Russia would beef up security for its forces in Syria, in what he called “steps that everyone will notice”.

Earlier Russian President Vladimir Putin called up Israeli Prime Minister Benjamin Netanyahu, reprimanding their military’s intrusion on Syrian sovereignty, Press TV reported on Tuesday.

He said that Israel has violated Syria’s sovereignty and has also negated Russian-Israeli agreements on the prevention of dangerous incidents.

Putin said that Russian Ilyushin II-20 aircraft came under fire of Syria’s anti-aircraft guns because of Israeli military’s aerial operations in Syria. He said that the belligerents used it as a ‘cover up’.

Syria is to blame for downing of plane, Netanyahu tells Putin

“The Israeli pilots used the Russian plane as cover and set it up to be targeted by the Syrian air defense forces,” the Russian Defense Ministry said in a statement on Tuesday.