The South Korean military fired two warning shots at a Russian military aircraft that entered South Korean airspace on Tuesday, the Ministry of National Defense in Seoul said, and Chinese military aircraft had also entered South Korean airspace.
It was the first time a Russian military aircraft had violated South Korean airspace, a ministry official said.
The warplane was one of three Russian aircraft to enter the Korea Air Defense Identification Zone (Kadiz) early on Tuesday. Two Chinese military aircraft also entered the Kadiz, the defence ministry said in a statement.
There was no immediate public comment from Russian or Chinese officials.
The South Korean government would lodge official complaints about the violations with China and Russia, the defence ministry in Seoul said.
According to the South Korean military, the Russian aircraft then violated South Korean airspace over Dokdo - an island that is occupied by South Korea and also claimed by Japan, which calls it Takeshima - just after 9am (midnight GMT Monday).
"The South Korean military took tactical action including dropping flares and firing a warning shot," the defence ministry statement said.
The Russian aircraft left South Korean airspace but then entered it again about 20 minutes later, prompting the South Koreans to fire another warning shot.
The ministry said South Korean warplanes "conducted a normal response" to the incursion, without giving further details.