The Russian Il-20 electronic intelligence plane of the Russian air force with the registration number RF 93610, which was accidentally downed by Syrian forces responding to an Israeli air strike flies near Kubinka airport, outside Moscow, Russia.

Russia announced Monday it will supply Syria's government with more modern, S-300 missile defence systems after last week's downing of a Russian plane by Syria, a friendly fire incident that sent regional tensions over the war-torn country soaring.

The Russian military's reconnaissance Il-20 was shot down by the Syrian government missile defence systems responding to an Israeli airstrike. All 15 people on board were killed. Russia laid the blame on Israel, saying Israeli fighter jets had pushed the plane into Syria's line of fire.

Syria's skies, where regional and international powers back different parties in the conflict, are increasingly crowded.

Shortly before the downing, Israeli strikes had hit targets inside Syria, reportedly preventing an arms shipment 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 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.

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Russian officials said Syria's outdated S-200 systems weren't sophisticated enough to identify the Russian plane as a friendly one.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 Damascus within the next two weeks. Earlier in the war, Russia suspended a supply of S-300s, which Israel feared Syria could use against it.