The aircraft remained on Estonian territory for about a minute, military spokespeople in Tallinn said. The aircraft's transponder was switched on, and a flight plan had been submitted, but there was no contact between the aircraft and Estonian Air Navigation Services at the moment the airspace violation took place.

The Estonian Foreign Ministry summoned the Russian ambassador to hand him a note of protest.

Tuesday's case is the sixth time this year a Russian aircraft violates Estonian airspace.

Most recently, a Sukhoi Su-27 fighter jet of the Russian armed forces entered Estonian airspace without permission in the area of the island of Vaindloo at 2:38 a.m. on Oct. 7 and spent less than a minute in Estonian airspace. The plane's transponder was switched off, it had not filed a flight plan, and it did not maintain radio contact with Estonian Air Navigation Services.

Prior to this, an incident took place on Sept. 5 when an Antonov An-72 of Russia's armed forces entered Estonian airspace again near Vaindloo Island and spent about one and a half minutes there. While its transponder was on, no flight plan had been submitted, and the plane was not in radio contact with Estonian Air Navigation Services.

On Jun. 7 and Mar. 28, Russian Antonov An-26 aircraft entered Estonian airspace without permission near Vaindloo, spending less than one minute in Estonian airspace. The planes, which had submitted flight plans according to which they were to fly in international airspace only, did not maintain radio contact with Estonian Air Navigation Services at the time of the incursion.

On Feb. 18 a Russian Mi-8 helicopter entered Estonian airspace without permission near the northeastern border guard base of Vasknarva. The helicopter stayed in Estonian airspace for less than one minute. The craft's transponder was switched off, and no flight plan had been submitted. There was no radio contact between the craft and the Estonian Air Navigation Services during the incident.

In 2015, aircraft of Russian armed forces violated Estonian airspace on three occasions. In 2014, the number of such incidents was eight, and most of them happened near the island of Vaindloo.