Estonia filed a protest with Moscow after a Russian aircraft violated the air space of the NATO ally and European Union member nation for the second time this year.

An IL-96 plane belonging to Russian Federation spent about one minute in Estonian airspace near the Baltic Sea island of Vaindloo, the military said.

The Russian plane’s transponder was on but the crew did not present a flight plan, according to Estonian authorities. The aircraft also did not maintain radio contact with the Estonian Air Navigation Service.

Russian Ambassador Alexander Petrov was summoned to the Estonian Foreign Ministry and officials presented him with a note about the violation, calling it a serious incident. They said the repeated occurrence of such air space breaches was in no way acceptable.