Russia's defence ministry said it had carried out air defence drills involving interceptor jets after St. Petersburg's Pulkovo Airport was forced to suspend all flights on Tuesday for an hour.
The government of Russia's second city announced the closure on its official Telegram channel without providing a reason for the suspension, as unconfirmed media reports said an unidentified object, such as a drone, had been spotted in the area.
City officials said later on Tuesday that flights had resumed and that a temporary airspace ban within a 200-kilometre (124-mile) radius of Pulkovo had been lifted by 1200 local time (0900 GMT).
In a statement issued around an hour after flights had restarted, Russia's defence ministry said it had been conducting drills, which had involved the despatch of fighter jets, in Russia's western air space.
"During the training, air defence forces worked on the detection, interception and identification of targets, as well as interacting with emergency services and law enforcement agencies," Russian news agencies cited the ministry as saying.
It said fighter plans had flown sorties as part of the training exercise. The drills were not previously announced and caused several flights to reroute and airlines to reschedule flight plans for the rest of the day.
Data from the FlightRadar24 website showed several flights headed for St Petersburg turning back to their destinations early on Tuesday, while the airspace closure also affected flights en route to the Russian exclave of Kaliningrad, which requires planes to fly over St. Petersburg.
By 1200 local time, flights had resumed flying towards St. Petersburg, and aircraft had recommenced landing and taking-off at the airport.
In a briefing after flights had resumed, Kremlin spokesman Dmitry Peskov declined to comment on the causes for the hour-long disruption, but said President Vladimir Putin had been kept fully informed of the situation.
(Reporting by Reuters; Writing by Jake Cordell;Editing by Andrew Osborn)
