Finland said on Thursday that its airforce would step-up "reconnaissance flights" after three violations of its airspace by Russian jets in less than a week.

According to a statement from the Ministry of Defence a "Russian plane of the type AN 72", which is a cargo aircraft, violated Russian airspace at midday on Thursday over the Gulf of Finland near the town of Porvoo, 25 miles (40 kilometres) east of the capital Helsinki.

The ministry reported two similar incidents on Saturday and Monday.

"We are obliged to increase reconnaissance flights," said Minister of Defence Carl Haglund, as quoted by Finnish public broadcaster YLE.

"It's hard to believe these are coincidences."

The minister said he would "demand explanations" from Moscow, according the Finnish newswire STT and confirmed that Finland dispatched a Hornet attack aircraft to identify the Russian plane.

Finland is a member of the European Union but not NATO and has an 800 mile (1,300 kilometres) long land border with Russia.

The country is part of NATO's Partnership for Peace, along with neighbouring Sweden.

On Thursday the Swedish government announced it would sign a pact reinforcing cooperation with the military alliance, a day after Finland said it intended to do the same.

The Host Nation Support agreement means both countries can host NATO training exercises and grant greater access to NATO troops on their territory.

Russia has repeatedly criticised any moves by Finland to join NATO, an issue which has been regularly debated in the Nordic nation.

Public opinion in Finland and neighbouring Sweden remains opposed to membership thanks to a traditional Nordic stance of non-alignment.