Finnish accession to the North Atlantic Treaty Organisation would "certainly" constitute a threat to Russia's security, and Moscow will analyse the consequences of such a step for its own security, Kremlin spokesman Dmitry Peskov has said.
"The latest expansion of NATO will not make our continent more stable and secure", Peskov said, speaking to reporters on Thursday.
"If you remember, there is an active instruction from the [Russian] president and commander-in-chief to develop a list of measures to strengthen our western flanks in connection with the strengthening of NATO's eastern flank. NATO is moving in our direction. Therefore, of course, all of this will become an element for a special analysis and the development of the necessary measures to balance the situation and ensure our security", Peskov noted, when asked how specifically Moscow might respond to Finnish membership in the US-led alliance.
"Everything will depend on how the expansion process will manifest itself in the future, how far military infrastructure will move closer to our borders", the presidential spokesman stressed.
Asked to comment on whether the Western bloc might try to use the Ukraine crisis as a pretext to incorporate even more countries bordering Russia, Peskov said that "a wide range of options is always being considered and analysed".
Earlier in the day, Finland's president and prime minister issued a joint statement saying that Helsinki "should apply without delay to join NATO", and that membership in the Western bloc would undoubtedly "strengthen" the Nordic nation's security.
Sweden is also expected to join the alliance, with reports suggesting Stockholm may formally apply for membership as soon as 16 May.
The two countries began discussing the possibility of abandoning their long-held neutrality earlier this year, in the wake of Russia's decision to launch a military operation in Ukraine to assist its Donbass allies. NATO chief Jens Stoltenberg welcomed the two countries with open arms in March, promising that the alliance would do everything to ensure that they are quickly incorporated.
Finland was one of the few countries in Europe that managed to enjoy neutrality throughout the second half of the 20th century and friendly political and economic relations with both the Western and Eastern blocs during the Cold War.
Sweden has maintained bloc neutrality for even longer, not taking part in any large-scale war since 1814. In the 20th century, the country was one of just a handful of European nations that managed to stay out of both the First and Second World Wars. During the Cold War, Stockholm formally maintained a policy of strict neutrality, although it has since been revealed that its forces would likely have taken part in an East versus West conflict on the NATO side.
Finland and Sweden joined NATO's "Partnership for Peace" programme in 1994. Both countries deployed troops in Afghanistan to support the NATO-led "Resolute Support Mission" occupation of the country. Forces from both countries have also been deployed in the NATO-led peacekeeping force in the Serbian breakaway region of Kosovo. Both nations have also taken part in various naval and air exercises with NATO from the 1990s onward.
Sweden and Russia do not share a land border. However, the two countries are about 250 km away from each other across the Baltic Sea and through Finnish Lapland. Finland and Russia share a 1,340 km long land border - one of the longest in Europe.
Last month, Russian Security Council deputy chairman Dmitry Medvedev warned that the two countries' entry into NATO would force Moscow to "seriously" strengthen its ground, air defence, and naval forces in the region, and "more than double" the existing land border between Russia and the Western bloc.
NATO has steadily expanded eastward for decades, notwithstanding promises to Soviet leader Mikhail Gorbachev in 1990 and 1991 not push beyond the borders of the reunited Germany following the German Democratic Republic's annexation by the Federal Republic in October 1990. Every member of the former Warsaw Pact alliance, plus three republics of the former Soviet Union, and four republics of the former Yugoslavia, have been incorporated into the bloc between 1999 and 2020.