The incident occurred near the Estonian island of Saaremaa, in the west of the country, a NATO spokesman in Brussels said. In response to the airspace violation, Portuguese  F-16 fighters were scrambled from a NATO airbase in Lithuania, which intercepted the Russian spy plane and escorted it out of Estonian airspace, Deutsche Welle said.

According to NATO, the Russian plane was heading towards Denmark and flew 600 meters into alliance airspace. In addition to the Portugese fighters, Danish and Swedish fighters were also scrambled during the operation.  The Russian plane is reported to have been in Estonian airspace for about one minute.

Meanwhile, Russia’s Ministry of Defence denied that one of its planes had violated Estonia’s airspace. The ministry said a Russian military plane “was carrying out a scheduled training flight... over neutral territories of the Baltic Sea." This was done in accordance with international rules about airspace use, the ministry said.

Estonia has summoned the Russian ambassador over the incident, which Tallinn regards as serious, and “demanded an explanation,” an Estonian Foreign Ministry spokeswoman said, according to U.S. broadcaster Voice of America.