It was the first time a Russian military plane violated South Korean airspace, according to South Korean officials.
The airspace the Russian plane violated was above a group of South Korean-held islets roughly halfway between South Korea and Japan that has been a source of territorial disputes between them.
Russia isn't a party in those disputes.
The three Russian planes had entered the South Korean air defence identification zone with two Chinese military planes.
But it wasn't immediately known whether the two countries deliberately did so, according to the South Korean official.
Before their joint flights with the Russian planes, the Chinese planes entered South Korea's air defence identification zone off its southwest coast earlier Tuesday, according to the South Korean official.
Chinese planes have occasionally entered South Korea's air defence identification zone in recent years.
South Korea's Defence Ministry said it plans to summon Russian and Chinese Embassy officials later Tuesday to register formal protests.
The ministry said South Korean warplanes "conducted a normal response" to the incursion, without giving further details.