The Russian military aircraft was downed by Syrian government missile defence systems, killing all 15 people on board. Russia laid the blame squarely on Israel, saying Israeli fighter jets had pushed the Russian plane into the line of Syria's fire.
Shortly before the downing, Israeli strikes had hit targets inside Syria, reportedly preventing an arms shipment going to the Iranian-backed militant Hezbollah group.
Russia launched its campaign in Syria to support President Bashar Assad in 2015, and though the involvement turned the tide of war in favour of Syrian government forces, Moscow has since tried to play a careful balancing act, maintaining good ties both with Iran and Israel.
For its part, Israel is wary of Iran's growing influence in Syria, which is bringing its archenemy closer to its borders. Last week's downing has put Russia's relationship with Israel to a test.
President Vladimir Putin initially struck a reconciliatory note, blaming the downing on a "chain of tragic, fatal circumstances." But the Russian military came out on Sunday, renewing the accusations against Israel.
Russian officials said Syria's outdated S-200 systems weren't sophisticated enough to identify the Russian plane as a friendly one.
Monday's statement from Russian Defence Minister Sergei Shoigu said Russia will send the S-300 missile defence systems to Syria within the next two weeks. Earlier in the war, Russia suspended a supply of S-300s, which Israel feared Syria could use against it.
Shoigu said Russia is now going to go ahead with the shipment because "the situation has changed, and it's not our fault." He also said that Russia would start to electronically jam aircraft flying in to attack targets in Syria.
"We are convinced that these measures will calm down some hotheads and keep them from careless actions which pose a threat to our troops," Shoigu said.
Russian Deputy Foreign Minister Mikhail Bogdanov told Russian news agencies that supplying S-300 to Syria is Russia's "own right" and expressed confidence that this would not hurt ties with Israel.
The Kremlin said Russia's decision was not targeted against anyone and only serves to protect Russian troops in Syria. Spokesman Dmitry Peskov told reporters that recent findings by the Russian military showed an Israeli jet "deliberately" pushed the Russian Il-20 into the line of fire, enabling its downing.
Putin tells Netanyahu he rejects Israeli version of plane downing
Russian President Vladimir Putin told Israeli Prime Minister Benjamin Netanyahu on Monday that he disagreed with the Israeli version of events concerning the downing of a Russian plane over Syria last week, the Kremlin said.
"The information provided by the Israeli military...runs counter to conclusions of the Russian defence ministry," the Kremlin said of the call, adding that the actions of the Israeli pilots had led to the plane being targeted by Syrian air defence systems.
"The Russian side proceeds from the fact that the actions by the Israeli air force were the main reason for the tragedy," a statement said.
Moscow said Netanyahu once again expressed condolences over the accident that killed 15 people.
Earlier on Monday, Moscow announced new security measures to protect its military in Syria, including supplying the Syrian army with an S-300 air defence system and jamming radars of nearby warplanes.
Putin told Netanyahu that the measures had been taken to prevent any threat to Russian troops in Syria.
Putin last week had adopted a more conciliatory tone and said the downing was the result of "tragic accidental circumstances".