MOSCOW — Russia’s Defense Ministry has spelled out why it believes a U.S. reconnaissance flight over the Sea of Japan was a safety risk, saying the plane risked colliding with civilian airliners.

The ministry has earlier summoned a U.S. military attached in Moscow to protest what it described as the “unprofessional” action of the U.S. crew during Sunday’s flight. The U.S. rejected the accusations, saying the flight was conducted safely in line with international law.

On Wednesday, Russian Defense Ministry spokesman Maj. Gen. Igor Konashenkov said the U.S. RC-135 aircraft repeatedly crossed the flight paths used by SWISS and KLM planes. He said the SWISS crew reported an unidentified plane approaching, and Russian air traffic controllers had to direct the Swiss plane to a lower altitude to avoid “catastrophic consequences.”