The air force said that the policing mission scrambled when the Russian aircraft was detected entering the Bucharest flight information region and heading toward Romanian airspace.
"The aircraft had not filed a flight plan & wasn't speaking to Romanian ATC so was deemed a flight safety hazard," the RAF tweeted.
The Typhoon jets were "airborne within minutes" and shadowed the Russian plane until it left the Bucharest flight information region, according to one of the pilots. The Su-24 had flown some 20 miles from the Romanian coast before being intercepted, after which the RAF fighters returned to the base, the statement said.