Finnish Defence Minister Antti Hakkanen rejected six permits for real estate transactions requested by non-EU and European Economic Area (EEA) buyers from Russia, Ukraine and Switzerland, the ministry said in a statement.

"It cannot be ruled out that the real estate acquisitions in question could threaten national security and hinder the organisation of national defence or the surveillance and safeguarding of territorial integrity," the ministry said.

It did not provide any explanation why the potential buyers could pose a security risk.

The attempted acquisitions, made by private individuals and one company, were for properties located in the southeastern Finnish towns of Mikkeli, Imatra, Kouvola and Lieksa.

Finland shares a 1,340-kilometre (830-mile) eastern border with Russia.

The six rejections come as Helsinki plans to tighten its legislation on foreign real estate transactions to prevent Russian citizens from purchasing property in Finland.

As part of the drafting process of a new bill, the defence ministry on Monday sent out a "report on banning foreign real estate acquisitions" for comments from experts.

According to the proposal, real estate permits should not be granted "to persons whose country of nationality has been found by the European Union to be in violation of the territorial integrity, sovereignty and independence of another country or whose country of nationality may be a threat to Finland's national security".

The ban would also apply to associations in such a country, it said.

Defence Minister Hakkanen said Monday that "Finland must make sure not to leave any windows of vulnerability open to hostile actors".