The Kremlin says NATO is already at war with Russia.
The Kremlin has claimed that NATO is "fighting against Russia" through its direct and indirect support for Ukraine.
"NATO is de facto involved in this war," Dmitry Peskov, a Kremlin spokesman, told reporters on Monday.
"NATO is providing direct and indirect support to the Kiev regime. It can be said with absolute certainty that NATO is fighting against Russia."
This comes as Russia violated the airspace of another NATO country, Romania, in the early hours of Sunday morning. The Romanian defense ministry scrambled two F-16 jets to shoot down a Russian drone in its airspace, just days after Poland confirmed an incursion by at least 19 Russian drones.
The Russian ambassador to Bucharest was summoned to protest against the "violation of Romania's sovereignty," Romanian Foreign Minister Oana Toiu said.
Ukrainian President Volodymyr Zelensky said a Russian drone traveled about 10 kilometers into Romanian territory and operated in NATO airspace for about 50 minutes before heading towards Ukraine.
He warned that the incident was "a clear extension" of Russia's war beyond Ukraine's borders and called once again for tougher sanctions against Moscow.
Meanwhile, the US military observed joint war exercises between Russia and Belarus on Monday.
This news was confirmed by Belarus' Defense Minister Viktor Khrenin, who said they could consider "anything that is of interest to them," Reuters quotes.
Russia and Belarus began the "Zapad-2025" exercise at training ranges in both countries on Friday at a time of high tensions with NATO, two days after Poland shot down Russian drones that crossed into its airspace.
The participation of Americans at a training ground in Belarus was presented by the country's defense ministry as a surprise.
"Who would have thought how the morning of another day of the Zapad-2025 exercise would begin?" she said in a statement, noting their presence among representatives from 23 countries, including two other NATO member states - Turkey and Hungary.
The ministry released a video showing two uniformed American officers thanking Khren for the invitation and shaking his hand.
"We will show whatever is of interest to you. Whatever you want. You can go there and see, talk to people," the minister told the Americans, who declined to speak to reporters.
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