But Putin, speaking in Moscow on Tuesday, rejected that Israel was to blame for the "friendly fire" incident as both Russian Federation and Israel raced to defuse tensions and prevent a major flare-up of tensions in southern Syria where both air forces operate.
The Russian military initially blamed Israel for the incident, claiming Israeli F-16 fighter jets used the IL-20 for cover.
Shedding further light on the incident, Syrian state media said that Latakia's capital of the same name came under attack from "enemy missiles" at around the time when the plane disappeared, forcing Syrian air defenses to respond.
Earlier on Tuesday, Russia's Defense Ministry said it held Israel responsible for the deaths of the 15 servicemen and promised to retaliate.
There was no immediate word from Damascus, but the deadly air war sequence started when missiles struck the coastal region of Latakia on Monday.
Defense Ministry spokesman Igor Konashenkov told the Russian state news agency TASS that Russia viewed "the provocative actions of Israel as hostile".
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"Hiding behind the Russian plane, Israeli pilots placed it for the fire of air defense of Syria", he said.
"The Israeli planes deliberately created a risky situation for surface ships and aircraft in the area", a defence ministry spokesman said.
"We reserve the right to take commensurate measures in response", Konashenkov said.
A search and rescue operation for the remains of the Russian plane was ongoing.
The military said Israel did not warn it of its operation over Latakia province until one minute before the strike, which did not give the Russian plane enough time to escape.
The US official, who spoke on condition of anonymity, said the US government's operating theory was that the Syrian defences accidentally shot down the Russian aircraft while firing at incoming Israeli missiles. "And these will be steps that everyone will notice", Putin said.
Syrian air defenses sprang to life during the attack, but it's unclear if they shot down anything besides the Russian Il-20.
The statement also laid blame on Iran and the Lebanese Shia militant group, Hezbollah, two other allies of the Syrian government.
Putin made his remarks several hours after the Defence Ministry put the blame squarely on Israel for "provoking" the incident.
Since intervening in Syria, Russia has turned a blind eye to these attacks. In some cases, those countries are backing opposing sides in the Syrian war.