Finland is in no position to help defend its Baltic neighbours and fellow EU members Estonia, Latvia and Lithuania should it become necessary, Finnish President Sauli Niinisto said on Tuesday.

His comments were made during talks with a group of Finnish ambassadors as regional tensions grow over the crisis in Ukraine.

"Every now and then we hear the idea that Finland could be partially responsible for the defence of the Baltics," Niinisto said.

"Finland is not in a position where it could offer others security guarantees which we ourselves don't even have."

Under Moscow's thumb until 1991, the three Baltic states have been on high alert since Russia annexed the Crimean peninsula from Ukraine last year.

Unlike its Baltic neighbours, Finland - which shares a 1,340-kilometre (830-mile) border with Russia - is not a member of NATO although the defence alliance has kept its doors open to the reluctant Nordic country.

"Our eastern border (with Russia) is longer than those of all NATO countries together. If a nation of a little over five million people is in charge of its defence on its own, it is enough responsibility to bear," Niinisto said.

Finland has tried to maintain good relations with its powerful neighbour since the end of World War II although it has lately observed an increase in Russian military activity in the Baltic Sea area.

But the regional tensions have not made Finnish public opinion more favourable to joining NATO, with recent polls showing a majority opposed.

Niinisto said Finland would continue to develop its own defence in cooperation with its western neighbour Sweden and through a partnership with NATO.