(Reuters) -- A Russian military jet almost collided with a commercial passenger airplane in international airspace near southern Sweden Friday, Swedish authorities said, but Russia insisted Sunday that its jet had kept at a safe distance.

Relations between Russia and the West have soured over Moscow's role in the conflict in Ukraine and its annexation of Crimea. Many European countries have reacted with alarm to suspected displays by Russia of its military prowess.

A squadron of Russian warships entered the English Channel last month, and Sweden said it had proof a foreign submarine was operating illegally in its waters in October. Britain also launched a submarine search, helped by NATO allies.

Friday's passenger flight SK1755 from Copenhagen in Denmark to Poznan in Poland was diverted by Swedish authorities before a collision occurred, the authorities said. The flight was operated by Cimber, owned by Scandinavian airline SAS.

Russia's Defense Ministry denied Sunday that its airplane had come close to colliding with a civilian airliner, the official news agency TASS reported.

"A flight was carried out in strict accordance with international rules on air space and did not violate the borders of other countries and was at a safe distance from the flight paths of civilian airplanes," Defense Ministry representative Gen. Maj. Igor Konashenko was quoted as saying.

Swedish military had said the Russian jet was flying with its transponder (a communications device that makes it easier for an airplane to be located) switched off, making it difficult for commercial traffic control to see it.

"The military aircraft had no transponder, but we discovered it on our radar and warned the civilian air traffic control in Malmo," Daniel Josefsson of the Swedish battle command center told the daily newspaper Dagens Nyheter Saturday.

"This is serious. This is inappropriate. It's outright dangerous when you turn off the transponder," Swedish Defense Minister Peter Hultqvist told Swedish radio Saturday.

NATO complained this month that Russian military aircraft are posing a threat to civilian planes by turning off communications devices and failing to file flight plans.

NATO warplanes have had to scramble 400 times this year in response to an increase in Russian air activity around Europe.

(Reporting by Johan Ahlander; Additional reporting by Thomas Grove in Moscow; Editing by Raissa Kasolowsky)