Finland has threatened to intercept Russian planes after they violated its airspace at least three times in the past week.
An Antonov An-72 transport plane crossed the Finnish border on Wednesday and two other Russian "state aircraft" breached the same space since 23 August.
Finland calls "state aircraft" those planes which are used in military, customs and police services.
"We will express the fact that from our perspective, this is totally unacceptable," defence minister Carl Haglund said, according to the online edition of newspaper Helsingin Sanomat.
"Three airspace violations within a week is a lot and unfortunately they don't really have a good explanation. What we know is they are done somewhat on purpose. We don't know what that purpose is," he said, adding that he will put Finnish air force on alert, according to Bloomberg.
The Finnish border guard said that in all three cases the Russian aircrafts ignored requests to leave the airspace.
The EU member has condemned Russian annexation of Crimea and alleged invasion of Eastern Ukraine. Finland and Sweden are due to sign a pact with Nato which will allow assistance from troops in case of an emergency, in instances such as "disasters, disruptions and threats to security".
Both countries have shied away from Nato full membership due to opinion polls showing opposition to it.
The North Atlantic Alliance is poised for a summit next week in Wales amid increased tensions with Putin's Russia over the crisis in Ukraine.
Finland was a part of the Russian Empire for 108 years but broke away in 1917 at the end of the First World War. It shares a 1,300km border with Russia and has stepped up surveillance due to the Ukraine crisis.
The Scandinavian country has collaborated with Nato since 1994 in terms of joining the Partnership for Peace program. It is hosting a two-week multinational military exercise including Nato and EU member states called Northern Coasts 2014, that started on Friday (29 August).
Helsinki has accused Moscow of violating its airspace five times since the Ukraine crisis started.