MOSCOW — The main bell in St. Isaac’s Cathedral in St. Petersburg tolled 224 times on Sunday, once for each victim of the destruction of a Russian charter flight in Egypt a week ago.

Although President Vladimir V. Putin and his aides at first indignantly dismissed suspicions of a terrorist act, the Kremlin has since then clearly come to grips with the idea that a bomb was probably involved in the crash: Late Friday it suspended all travel by Russians to Egypt, and initiated an emergency airlift that by Sunday had repatriated 11,000 Russians, by government count.

Should an attack be confirmed — and particularly if the Islamic State’s claim that it bombed the plane in revenge for Russia’s intervention in Syria turns out to be true — analysts and other experts expect that it will only strengthen Mr. Putin’s resolve to become more deeply involved in the Middle East.

First, Mr. Putin said the Russian Air Force’s bombing campaign in Syria was partly intended to help dismantle the Islamic State, also known as ISIS or ISIL, which includes up to 7,000 fighters from Russia and the former Soviet Union. One worry is that they might return to wage a terrorist war in Russia. An attack against a civilian airliner would confirm that Russian interests were already being threatened — and might cause Russia to begin targeting the Islamic State more aggressively.