Finland and Sweden will become "targets" for Moscow if they join NATO, warned the Russian ambassador in Stockholm.
After their accession, "the total length of the borders between Russia and NATO will almost double", Ambassador Viktor Tatarintsev said on Tuesday.
"If it still seems to anyone that this will somehow improve Europe's security, rest assured that the new members of the hostile bloc will become a legitimate target for Russian retaliatory measures, including those of a military nature", he added.
Russia has repeatedly threatened the Nordic pair after they submitted bids to join the western military alliance last May, following the outbreak of war in Ukraine.
Though closely allied with NATO for more than two decades, the two were not formal members of the military alliance, and public opinion was firmly against joining.
That all changed after Russia invaded Ukraine, when public opinion swung dramatically in favour of joining NATO -- at one point topping 80% in Finland which shares a 1,300km border with Russia -- and nearing two-thirds support in Sweden, according to polls.
Under NATO rules, a country only becomes a full member when all 30 countries have ratified their applications.
Finland is now waiting for Turkey to ratify their bid to join NATO, something that President Recep Tayyip Erdogan has promised to do.
Hungary, the only other country to drag its heels, ratified on Wednesday and is expected to drop the instrument of ratification in Washington DC on Friday.
As for Sweden, its candidacy is still in question. Ankara is currently blocking its entry, while Hungary is delaying ratification.
Both countries are widely seen as biding their time to extract political concessions from Stockholm, and in the case of Hungary, from the EU; while Turkey also hopes to leverage advantageous access to military programmes from the US.
However, officials in Sweden still hope to join before the next NATO summit in July in Lithuania.
But for the Russian ambassador in Stockholm, who was born in Kherson in present-day Ukraine, Sweden is taking "a step into the abyss" by wanting to become a member.
Criticising its "hasty" decision without a national referendum, he claimed the NATO command had "decided to enter fully into the conflict", creating risks for Sweden.
"In this case, the Swedes will undoubtedly be drawn in and sent to their deaths for the interests of others," Tatarintsev wrote.