Tallinn: Estonia, on Friday, summoned a Russian diplomat after three Russian military aircraft entered its airspace without clearance and remained for 12 minutes, the Foreign Ministry said.

Foreign Minister Margus Tsahkna condemned the incident, calling it the most serious breach this year.

“Russia has already violated Estonian airspace four times this year, but today’s incursion, involving three fighter aircraft entering our airspace, is unprecedentedly brazen,” he said.

According to the ministry, the violation occurred over the Gulf of Finland and involved three Russian MiG-31 fighter jets.

The Russian charge d’affaires in Tallinn was summoned and handed a formal protest note, the ministry added.

Last week, the Russian incursion into Poland, which caused NATO to send fighter jets to shoot down the drones, heightened tensions in Eastern Europe about Moscow's territorial ambitions. The war between Russia and Ukraine has continued despite months of U.S. efforts to stop it, including a U.S.-Russia summit meeting in Alaska.

NATO announced it was strengthening its defensive posture on its eastern flank bordering Belarus, Russia and Ukraine. Moscow, meanwhile, showcased its conventional and nuclear military power in long-planned exercises with Belarus that fueled Western concerns about Russia's intentions.

The Ukrainian and Polish government ministers also signed in Kyiv an agreement to work together more closely on defence.