Poland has prevented a plane carrying Russia's defense minister from traveling through its airspace, leading to a complaint from Moscow.

The incident comes at a time of tension between the two countries because of Russia's support for separatists fighting in Ukraine.

The Russian Tu-154 plane was carrying Defense Minister Sergei Shoigu home from Slovakia Friday when it was barred from Polish airspace, said Polish military spokesman Lt. Col. Piotr Walasek. He said that probably happened because the Russian pilot mistakenly reported his flight was a military one, not the civilian one for which he had permission.

But the Interfax news agency quoted Russian First Deputy Foreign Minister Vladimir Titov as saying the Russian Foreign Ministry considers Poland's move a "gross violation of the norms and ethics of communication between states."