MOSCOW, Sept. 18 (Xinhua) -- Russian President Vladimir Putin said Tuesday the downing of the Russian Il-20 surveillance plane was the result of "a chain of tragic and random circumstances" and Russia will beef up security measures for its soldiers.

The incident on Monday night was different from Turkey deliberately shooting down a Russian jet in November 2015 as Israel did not attack the Il-20, Putin said at a joint press conference with visiting Hungarian Prime Minister Viktor Orban.

"But, no doubt, we have to investigate this seriously," he said, adding that Russia in response will provide additional security to its troops in Syria.

Putin expressed condolences to the relatives of those who had perished in the tragedy.

The Russian Defense Ministry said earlier in the day that the Il-20 plane with 15 servicemen on board was mistakenly downed by a Syrian missile due to a simultaneous Israeli air strike that confused Syria's air defense system.

The ministry said the Israeli jets used the Il-20 as a shield and called the provocative actions of Israel hostile.