"Two Russian MIG-31 fighters are suspected of having violated Finnish airspace in the Gulf of Finland off Porvoo," the ministry said in a statement.

The Finnish Air Force sent up "an operational flight mission" to identify the aircraft, it said, adding that the Finnish Border Guard had started "a preliminary investigation".

The incident occurred at 9:40 am (0640 GMT) and lasted about two minutes as the jets flew westward for about one kilometre, a defence ministry spokesman told AFP.

Finland, which shares a 1,300-kilometre (800-mile) eastern border with Russia, reversed decades of military non-alignment by seeking membership in the North Atlantic alliance in May, after being rattled by Moscow's invasion of Ukraine.

The Finnish Security and Intelligence Service (SUPO) warned in May that "Russia has the will" to influence Finland's NATO application process and that "various attempts to do so are to be expected".