A number of Russian domestic flights headed for St. Petersburg were turning back to their departure points on Tuesday, according to the Flight Radar flight tracking website.
At least five flights en route from the capital Moscow to St. Petersburg had been turned back towards Moscow as of 1100 local time (0800 GMT), after initially circling in the air, flight paths on Flight Radar showed.
It was not immediately clear why though an unconfirmed media report from online Russian news outlet Baza said an unidentified object had been spotted in the sky and that fighter jets had been despatched to investigate.
