His intervention risks provoking fresh tensions a day after Moscow and Tel Aviv moved to de-escalate a row that threatened to build into a military confrontation.
This unfortunate incident was the result of Israeli arrogance and depravity, the Syrian leader said, offering his condolences in a letter to his Russian counterpart for the death of 15 Russian crew members killed in the incident over Syria on Monday.
We are determined that such tragic events will sway neither you nor us from continuing the fight against terrorism, he continued in the letter published by the official Sana agency.
The Russian plane was shot down by Syria’s Russian-made S-200 air defence system and all aboard were killed on Tuesday.
The Russian military has accused Israeli pilots of using the Russian plane as cover, exposing it to fire from Syrian air defences while they mounted an air raid.
It was the worst friendly fire incident between Moscow and the Syrian regime since Russian forces intervened in the country in late 2015 to support Mr Assad whose grip on power had been weakened by rebels and jihadist fighters.
Vladmir Putin, the Russian president, had struck a conciliatory tone a day earlier describing the incident as the result of tragic accidental circumstances, but warning Benjamin Netanyahu, the Israeli prime minister, against carrying out such operations in the future and promiding to beef up security for Russian forces in Syria.
However he insisted the Russian plane had been felled by extensive and inaccurate Syrian anti-aircraft (fire).
In recent months Israel has increased its attacks in Syria against the regime or its ally Iran.