Russian President Vladimir Putin has warned Finland that relations between the two countries could be in trouble after the Nordic country joins NATO.

"There were no problems. Now there will be. We're going to create the Leningrad military district (northwest) and concentrate military units there. Did they need that? It's simply absurd," Putin said in statements to the Moscow TV program.

According to Notícias ao Minuto, Putin pointed out that all the territorial disputes between the two countries were resolved in the middle of the 20th century, which is why he regretted that Finland had been dragged into NATO.

Moscow wants to strengthen its northwestern flank, especially the region around the country's second city, St. Petersburg, which is only about 300 kilometers from the Finnish capital, Helsinki.

The Kremlin has already warned this week that the deployment of US troops on Finnish territory would be an obvious threat to Russia.

Finland and the United States have reached a cooperation agreement that will allow US troops to use 15 military bases in the Nordic country.

Finland, the EU country with the longest border with Russia (1,340 kilometers), opted to abandon its traditional policy of neutrality after the start of Russia's military campaign in Ukraine and completed its entry into NATO in April.