SEOUL, South Korea — South Korea said its air force jets fired hundreds of warning shots on Tuesday to ward off a Russian military plane that intruded upon what it considers its territorial airspace, the first such encounter between the countries in decades.

The incident came as Russia and China conducted what Russia called a joint air patrol in the Asia-Pacific. South Korea said that three Russian military planes, as well as two Chinese warplanes, entered its air defense identification zone off its east coast, where foreign military aircraft are expected to identify themselves in advance to South Korea.

But South Korea said that one of the Russian planes, a Beriev A-50 early warning and control aircraft, flew closer and intruded twice into what the South regards as its territorial airspace, near a cluster of disputed islands that South Korea controls but Japan also claims.

Both times, the Russian plane violated that territorial airspace for a few minutes, prompting South Korean F-15 and F-16 fighter jets operating nearby to fire 20 flares and 360 machine gun rounds as warning shots from a half mile away, the officials said. The South Korean jets took the action after the Russian plane did not answer repeated radio warnings, according to the South.