Three Russian MiG-31 fighter jets violated Estonian airspace for 12 minutes on Friday, Estonia's government said in a statement.
Estonia summoned a Russian diplomat to protest, the Foreign Ministry said.
Foreign Minister Margus Tsakhna said that Russia had already violated Estonian airspace four times this year “but today's incursion, involving three fighter aircraft entering our airspace, is unprecedentedly brazen”.
His ministry said that the incursion took place over the Gulf of Finland.
The Russian charge d'affaires was summoned and given a protest note, a ministry statement said.
NATO responded immediately and intercepted the Russian jets which violated Estonian airspace, a NATO spokesperson said in a statement on social media X on Friday.
"This is yet another example of reckless Russian behaviour and NATO’s ability to respond," the spokesperson said.
The violation of NATO member Estonia's airspace by three Russian military jets on Friday was an "extremely dangerous provocation", the EU's foreign policy chief Kaja Kallas said.
"This marks the third such violation of EU airspace in days and further escalates tensions in the region," Kallas said in a post on X. "We will continue to support our member states in strengthening their defences with European resources. Putin is testing the West's resolve. We must not show weakness."
Russia's violation of Poland's airspace was the most serious cross-border incident into a NATO member country since the war in Ukraine began with Russia's all-out invasion in February 2022. Other alliance countries have reported similar incursions and drone crashes on their territory.
The developments have increasingly rattled European governments as US-led efforts to stop the war in Ukraine have come to nothing.
Estonia, along with other Baltic states Lithuania and Latvia, are seen as being among the most likely targets if Russia one day decides to risk an attack on NATO. Neighbouring Poland, though much larger, also feels vulnerable. All four countries are staunch supporters of Ukraine.