Russia has threatened it will mobilize its forces to areas closer to its border with Finland should Helsinki choose to join the US-led military alliance of NATO.

“Do you think we will continue to act in the same manner [if Finland joins NATO]?” visiting Russian President Vladimir Putin asked at a joint press conference with his Finnish counterpart Sauli Niinisto at the latter’s summer residence in southwestern Finland on Friday.

“We have withdrawn our troops 1,500 [kilometers (932 miles) from the border]. Do you think they will stay there?” Putin said.

Back in April, Russian Foreign Minister Sergei Lavrov had likewise said that Russia would take appropriate military-technical measures at its northern borders if Finland’s neighbor Sweden decided to join NATO.

Already reeling from mutual distrust, relations between Russia and NATO specially soured after the Black Sea Crimea Peninsula rejoined the Russian Federation from Ukraine following a referendum in March 2014.

The United States and its European allies accuse Moscow of destabilizing Ukraine and have imposed sanctions against Russian and pro-Russia figures. Moscow, however, rejects having a hand in the Ukrainian crisis.

In his Friday remarks, Putin said Moscow will try to begin a dialogue with NATO despite its expansion towards Russia’s western borders.

He said Moscow would, however, respect Helsinki’s decision in case it opted to join the Western alliance.

The Russian head of state also welcomed a proposal by the Finish president that aircraft flying over the Baltic region turn the devices enabling their identification on, calling it “the first steps aimed at enhancing confidence and preventing conflicts [in the Baltic airspace].”

RT said Russia had intercepted several US aircraft over the Baltic Sea in close proximity to the country’s border in recent months. The planes in question had their identification devices turned off, Moscow has complained.

Russia has repeatedly censured the gradual expansion of NATO eastward.

NATO routinely engages in activities deemed provocative to Russia. The alliance has installed missile systems across Europe, including ones recently launched in its eastern flank near Russia, and is involved in military exercises in Ukraine, another Russian neighbor.