The Syrian air defences were attempting to target Israeli F-16 jets, according to Russian military.
Prime Minister Benjamin Netanyahu on Monday spoke by telephone with Russian President Vladimir Putin and expressed his confidence in the credibility of the IDF investigation and its conclusions, reiterating that the Syrian military, which brought down the plane, and Iran, whose aggression is undermining stability, are responsible for the unfortunate incident.
The messages underscore the complexities facing U.S. policymakers as they deal with the various conflicts that have ripped Syria apart since 2011, and how deeply the U.S., Russia, Iran and Israel have been drawn into the conflict that began as street protests against the Assad regime.
But when the dust settled, blame fell on Israel.
Russian Defence Minister Sergei Shoigu announced that the S-300 missile defence systems will be delivered to Damascus within two weeks.
"We think introducing the S-300s to the Syrian government would be a significant escalation by the Russians", US national security advisor John Bolton said on Monday, adding: "and something that we hope if these press reports are accurate, they would reconsider".
"In regions near Syria over the Mediterranean Sea, there will be radio-electronic suppression of satellite navigation, on-board radar systems and communication systems of military aviation attacking objects on Syrian territory", he said.
"The situation has changed, and not due to our fault", the statement said.
Israel maintains that indiscriminate fire from Syrian forces was to blame for the incident.
A Russian Defense Ministry spokesman on Sunday stated that "objective data says that the actions of Israeli pilots, which led to the death of 15 Russian military personnel, point to either lack of professionalism or criminal negligence".
The Kremlin blamed Israel for the attack and vowed to sell S-300 air defence missile systems to its allies in Damascus.
An Israeli official said the information showed that the Russian plane was shot down because Syrian batteries had "fired recklessly, irresponsibly and unprofessionally, long after our planes were no longer there".
Israel denied this version of events and its air force commander flew to Moscow following the incident, which Putin called the result of a "chain of tragic accidental circumstances".
Kremlin spokesman Dmitry Peskov told reporters the decision to supply the weapons was not directed at any third country.
Israel says it is determined to stop Iran, a longtime foe that has sent forces to back Assad, from becoming entrenched near Israel's northern border and prevent the transfer of advanced missile systems to Iranian proxies, including Hezbollah.