Commander of the Raja Haji Fisabilillah Air Base in Tanjungpinang, Col M Dadan Gunawan, said here that the foreign aircraft was driven out through visual contact.
"The effort to drive them out through radio communication failed, and then we made visual contact," Gunawan noted.
According to Gunawan, the authority need not force the foreign aircraft to land if it has agreed to go out of the country`s territory.
However, the Air Force would force them to land in Hang Nadim Airport in Batam if it refused to leave the Indonesian territory.
"Based on our preliminary assessment, the foreign aircraft was conducting a test flight. Maybe it had just finished its maintenance," he remarked.
Gunawan did not elaborate further on the type and owner country of the aircraft but stated that the authority has documented the incident.
The two Sukhoi warplanes are still patrolling in the area around Riau Island.
Reporting by Nikolas Panama
Editing by Sri Haryati, Yoseph Hariyadi