An Air Serbia operating a scheduled flight from Istanbul to Belgrade has declared a general emergency and is on a return to Istanbul.
Air Serbia flight JU803 operated by an Airbus A319, registered YU-APK, departed Istanbul (IST) enroute to Belgrade Nikola Tesla Airport (BEG).

The aircraft was outbound to Belgrade and on climb through FL210 (21,000 feet) before declaring a general emergency, squawking 7700 before executing a return to Istanbul.
The nature of the emergency has not yet been ascertained.

This is a developing story. Please check back for updates.