Two Nordic countries are on the brink of allying with NATO, a move that Russia brands as a direct threat. Moscow also warned about possible rotation through unspecified military-technical measures.

Finland on Thursday said that it would apply to join NATO without delay. Sweden is expected to follow with the Russian invasion of Ukraine, moves that Russian leader Vladimir Putin reportedly aimed to prevent.

If made official, the decision of Finland and Sweden to abandon their neutrality could be a crucial shift in European security for decades.

This developed even as Russia suffered another setback after Ukrainian forces drove Russian troops out of Kharkiv. It was the fastest advance of Ukraine since it forced Moscow to withdraw from the capital and northeast over a month ago.

NATO Secretary-General Jens Stoltenberg said the Finns would be "warmly welcomed" and promised a "smooth and swift" accession process, Reuters reported.

Should Finland and Sweden join NATO, this would be telling.

Finland's 1,300-km border will more than double the length of the frontier between the U.S.-led alliance and Russia.

"Finland must apply for NATO membership without delay," President Sauli Niinisto and Prime Minister Sanna Marin said in a joint statement, hoping steps to take the decision would "be taken rapidly within the next few days".

When asked if this move would be a direct threat to Russia, Kremlin spokesman Dmitry Peskov said that this is definitely the case.

"Definitely. NATO expansion does not make our continent more stable and secure,” Peskov stated. "This cannot fail to arouse our regret, and is a reason for corresponding symmetrical responses on our side."

Russia’s foreign ministry claims that Moscow would take retaliatory steps, saying that this would be both military-technical and other nature. Other than that, no further details were given.

As far as Finnish President Sauli Niinisto is concerned, this alliance was provoked no less by Putin.

"My response would be that you caused this. Look at the mirror," Niinisto said.

Vladimir Putin Russia's President Vladimir Putin listens during his meeting with "Znanie" Society CEO Maxim Dreval in Moscow's Kremlin on May 5, 2022. Photo by Mikhail Klimentyev/Sputnik/AFP via Getty Images