Moscow has denied claims of an incursion by a Russian military plane into Estonia's airspace.
A Russian Defense Ministry spokesman told Interfax news agency on October 23 that the Ilyushin-20 took off from Khrabrovo airfield in the Russian exclave of Kaliningrad on October 21.
The spokesman said the reconnaissance plane flew "over neutral waters of the Baltic Sea" while on a training flight.
On October 22, Estonia’s Foreign Ministry summoned the Russian ambassador in Tallinn, Yury Merzlakov, after the Estonian military said the Russian plane had entered its airspace.
In a statement, NATO said the Ilyushin-20 was first intercepted by Danish jets when it approached Denmark, before flying toward non-NATO member Sweden.
Intercepted by Swedish planes, the alliance said the Ilyushin entered Estonian airspace for “less than one minute” and was escorted out by Portuguese jets.
NATO has stepped up its Baltic air patrols and Moscow has been accused of several recent border violations in the region amid heightened tensions between Russia and the West over the Ukraine conflict.
Last month, Estonia accused Russia of abducting one of its police officers on the border.
Russia claim Eston Kohver was seized inside Russia on September 5, while Estonian officials say he was captured at gunpoint near the border and taken to Russia.
The European Union and United States have called for the immediate release of the Estonian security official, who is facing espionage charges in Russia.
Meanwhile, the Swedish Navy has been searching for a suspected submarine sighted six days ago some 50 kilometers from the capital, Stockholm, although it said on October 22 it was pulling back some of its ships.
Swedish officials have not linked any particular country to the suspected intrusion and Moscow has denied involvement.