A flight en route from St. Petersburg, Russia, to Kaliningrad, the capital of the country’s westernmost exclave, returned to the airport of departure after a fire alarm went off, a Rossiya Airlines spokesperson told TASS.

"A fire alarm indicator went off on Flight FV6323, en route from St. Petersburg to Kaliningrad, during ascent. The aircraft returned to the airport of departure," the official said.

Technicians are now working to establish the cause of the incident. Neither smoke nor a burning smell was reported.

"The passengers departed on a replacement aircraft," the spokesperson added.