Two Russian MiG-31 fighter jets reportedly violated the Finnish airspace near the coastal city of Porvoo on the Gulf of Finland on Thursday.
The incident came as Finland seeks NATO membership following Russia's invasion of Ukraine.
The incident of suspected violation happened at 06:40 GMT on Thursday and the jets were westbound, the defence ministry's communications chief Kristian Vakkuri said, adding the aircraft were in Finnish airspace for two minutes, Al Jazeera reported.
"The depth of the suspected violation into Finnish airspace was one kilometre," Vakkuri said.
In order to tackle the suspected violation, the Finnish air force sent up "an operational flight mission" and identified the MiG-31 jets.
The Border Guard launched an investigation into the violation, reported Al Jazeera.
Finland, which shares a 1,300-km eastern border with Russia, broke decades of military non-alignment by seeking membership in the North Atlantic alliance in May.
Finland and Sweden's accession to NATO would mark one of the biggest shifts in European security in decades and further increase Russia's strategic isolation.
According to a NATO list, seven-member countries are yet to give a nod to the new double-entry: the Czech Republic, Greece, Hungary, Portugal, Slovakia, Spain and Turkey, according to Al Jazeera.
Earlier, North Atlantic Treaty Organisation's (NATO) 30 allies signed accession protocols for Sweden and Finland, kickstarting the process to admit the two Nordic countries into the alliance.
NATO's 30 members formally invited Finland and Sweden to join their alliance at the NATO Summit in Madrid, Spain, just seven weeks after both countries handed their applications in response to the Russia-Ukraine conflict.
In the first instance, the accession process was blocked by Turkey, a NATO member that raised concerns over the fight against terrorism, however, after signing a memorandum of understanding (MOU) with Finland and Sweden, Turkey lifted its veto ahead of the NATO Madrid summit.
( With inputs from ANI )
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