Estonia, a NATO member, said a Russian Mi-8 helicopter crossed into its airspace on Saturday.
The intrusion came days before a major NATO summit in Madrid, Spain.
Putin has long seen NATO as a threat, citing it as justification to invade Ukraine this year.
Estonia, a NATO country, said a Russian military helicopter briefly crossed into its territory last Saturday, suggesting Russia was further threatening the military bloc and lashing out at its closest neighbors.
Estonia's defense ministry said on Tuesday that a Russian Mi-8 helicopter entered the region of Koidula without permission for two minutes on Saturday, adding that it was one of several recent aerial intrusions by Russia.
Kusti Salm, the ministry's top civil servant, said Russia was simulating missile attacks against Estonia with the threat to the country at an all-time high, Sky News reported.
The helicopter intrusion into Estonia came days ahead of a major NATO summit in Madrid, Spain, set to be held on June 29. NATO members are expected to discuss how the bloc can strengthen in response to Russia's invasion of Ukraine.
Russian President Vladimir Putin has long remonstrated that NATO's expansion poses a threat to Russia, and he used it as a justification to invade Ukraine earlier this year.
In May, Russia's neighbor Finland — which that month applied to join NATO in light of Russia's invasion — said that a Russian Mi-17 helicopter entered its airspace but that it was not a serious provocation.
Russia is also threatening Lithuania, another of its neighbors.
Earlier this week, Lithuania, a member of NATO and the European Union, refused to let Russian steel and iron-ore materials pass through its territory to the Russian enclave of Kaliningrad, telling Moscow it would be violating EU sanctions if it did.
Following Russia's invasion of Ukraine in February, the EU barred member states from letting an array of Russian exports — including coal, metals, construction materials, and tech goods — into the bloc.
Nikolai Patrushev, the secretary of Russia's Security Council, said the decision to block goods "will have a serious negative impact on the population of Lithuania."
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