Finland has alleged that Russian fighter jets have entered into its airspace twice over the Baltic Sea on the same day.

The Finnish Ministry of Defence said that two different Russian SU-27 fighters have been detected in the Gulf of Finland south of Porvoo on 6 October.

The first suspected violation occurred at 16:43 local time on Thursday, while the second event took place in the same area at 21:33.

"Having two suspected violations on the same day is exceptional."

Finland Minister of Defence Jussi Niinisto was quoted by Reuters as saying: "We take these incidents seriously.

"Having two suspected violations on the same day is exceptional.”

According to the ministry, the first SU-27 aircraft stayed in the French airspace for nearly one minute 'for about 13km at a maximum of about 1km depth'.

The Finnish Air Force has conducted an identification flight.

'During Thursday the Russian military aviation over the Baltic Sea has been intense', the ministry said.

An investigation into the incidents will be launched by the Finnish Border Guard.

Russia, however, denied allegations from Finland that its SU-27s were involved in violation.

RIA news agency quoted Russian Defense Ministry as saying: "The plane did not veer off its route during the flight, which is confirmed by data of the control monitor system.”