US President Joe Biden on Thursday reiterated that a Russian invasion of Ukraine could take place any time, and ruled out having any further telephonic conversations with his Russian counterpart, Vladimir Putin.

While departing the White House on Thursday morning, Biden told reporters that he had “reason to believe” that Russia had conducted a “a false flag operation.”

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“Every indication that we have is that they are prepared to go into Ukraine, attack Ukraine. My sense is it will happen within the next several days,” Biden added.

The 79-year-old went on to say that he had “no plans to call Putin” but added that “there is a path” to diplomacy in the Ukraine crisis, referring to US Secretary of State Anthony Blinken’s visit to the United Nations (UN) on Thursday to chart out a diplomatic solution.

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Biden’s statement on Russia’s intentions comes on the back of Russia’s formal response to the US and NATO’s proposals on the security guarantees demanded by Moscow.

“We can confirm that we have received a response from the Russian Federation. It was delivered to Ambassador Sullivan in Moscow today,” reported CNN on Thursday, citing a senior US State Department official.

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NATO’s proposed solution to Russia’s security demands, submitted to Moscow three weeks ago, had charted “out a serious diplomatic path forward” as per Blinken, but Russia’s foreign minister Sergey Lavrov said on Thursday that NATO’s proposition was inadequate.

Speaking in Italy after his meeting with the Italian Minister of Foreign Affairs, Luigi Di Maio, Lavrov told the press that the Ukraine crisis would not be resolved “until we agree on our key positions.”

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“That is NATO’s non-expansion to the East, non-placement of the strike weapons, and respect to the military and political configuration at the time of signing of founding act between Russia and NATO,” Lavrov said, highlighting Moscow’s core demands.

Moscow on Thursday also announced a second troop withdrawal, and has countered Western allegations about being deceptive, saying that a troop withdrawal has a schedule and takes time.