The Finnish border force has launched an investigation into reports that two Russian MiG-31 fighter jets infringed on Finnish airspace on Thursday morning. The two jets were reported in the Gulf of Finland, near the city of Porvoo.
The suspected violation of Finnish airspace was reported at 6.40am GMT.
Finnish communications chief Kristian Vakkuri told Reuters that the aircraft were believed to have been travelling westbound.
He added: “The depth of the suspected violation into Finnish airspace was one kilometre.”
On Thursday, the Russian Interfax news agency reported the Russian defence ministry had relocated three of its MiG-31 warplanes.
The planes, carrying Kinzhal hypersonic missiles, were to be moved to Kaliningrad, the agency added.
The Baltic Sea base is sandwiched between Lithuania and Poland, which are both members of NATO.
Finland, along with Sweden, broke a long-held foreign policy staple of non-alignment earlier this year to apply for NATO membership.
The move came as a direct response to Vladimir Putin’s invasion of Ukraine.
READ MORE: ‘HIMARS time!’ Putin rattled by humiliating video
The Russian leader said their accession to the alliance would force Moscow to “restore military balance”.
Russia’s deputy foreign minister, Sergei Ryabkov, said: “We condemn the irresponsible course of the North Atlantic Alliance that is ruining the European architecture, or what’s left of it.”
He added: “I have a great deal of doubt as to whether the upcoming period will be calm for our north European neighbours.”
Earlier this week, Helsinki announced it would limit the number of visas granted to Russian applicants.
Finland’s foreign minister, Pekka Haavisto, said the measure would come into effect on September 1.
It comes after an influx of Russian tourists bound for Europe, with Finland one of the few border crossings still available to inbound Russian aircraft.