A Russian military helicopter entered Estonian airspace without permission Saturday, flying above the Koidula region along the Russia border for about two minutes, Estonia's defense ministry said in a statement Tuesday.
A flight plan was not filed, the transponder was switched off and two-way radio communication was not established with Estonian air traffic control, the ministry said.
Russia's ambassador to Estonia Vladimir Lipajev was summoned by Estonia's foreign affairs ministry. "Estonia considers this an extremely serious and regrettable incident that undoubtedly causes additional tensions and is completely unacceptable," the foreign affairs ministry said Tuesday.
Estonia is a nation of less than 3 million people that broke from the Soviet Union in 1991.
Ukrainian President Volodymyr Zelenskyy's adviser, Oleksiy Arestovych, said via social media Monday that Ukraine is under threat of a new Russian attack of large proportions, posting: "All six carriers of Russian cruise missiles lined up in the Black Sea and are most likely preparing for a massive launch of missiles.''
In a nightly address Sunday, Zelenskyy warned of a likely offensive coming from Russia this week, when the European Union will debate whether to make Ukraine an official candidate to eventually join the bloc.
"Obviously, we should expect greater hostile activity from Russia. Purposefully, demonstratively. This week exactly,'' Zelenskyy said. "And not only against Ukraine, but also against other European countries. We are preparing. We are ready. We warn partners.''
If they do launch an attack, the Russians could be retaliating for Ukrainian missile strikes Monday on three drilling rigs in the Black Sea that supply natural gas to Crimea, the Ukrainian peninsula the Kremlin illegally annexed in 2014. The state-owned TASS news agency reported the strikes caused injuries. The Ukraine military has not provided confirmation.