Washington-Moscow tensions are at their highest since the Cold War, with some U.S. estimates displaying 130,000 Russian soldiers are grouped in dozens of fighting brigades near the border with Ukraine.
"American citizens should leave now," Biden announced in a pre-taped interview with NBC News.
"We're dealing with one of the largest armies in the world. It's a very different situation, and things could go crazy quickly."
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Biden reiterated that he would send U.S. troops to Ukraine under no circumstances, even to rescue Americans in case of a Russian invasion.
"That's a world war. When Americans and Russians start shooting one another, we're in a very different world," he stated.
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Biden's comments were released hours after Russia rolled its tanks across Belarus for live-fire drills that drew an ominous warning from NATO and added urgency to Western attempts to prevent war on the continent.
NATO stated that Russia's deployment of missiles, heavy armor, and machine-gun toting soldiers marked a "dangerous moment" for Europe some three decades after the Soviet Union's collapse.
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Western leaders have been shuttling to Moscow to keep the lines of communication open, allowing Russia to air its grievances about NATO's expansion into eastern Europe and ex-Soviet states.
But they have attempted to project their resolve in the face of Russian escalation of an already-tense situation.
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"Russia should not underestimate our unity and determination as a partner in the EU and as an ally in NATO," German Chancellor Olaf Scholz cautioned.
In an attempt to "reduce chances of miscalculation" throughout the drills, U.S. and Belarusian defense chiefs held rare telephone talks, the Pentagon stated Thursday.
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Russia has sent six warships through the Bosphorus for naval drills on the Black Sea and the neighboring Sea of Azov.
Kyiv condemned their presence as an "unprecedented" effort to cut off Ukraine from both seas.
Moscow and Minsk have not disclosed how many troops are participating. Yet, the United States has announced that roughly 30,000 soldiers were being dispatched to Belarus from locations including Russia's Far East.
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Russia's defense ministry insisted the exercises would center around "suppressing and repelling external aggression" and the Kremlin has promised the troops will go home after the exercises.
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Though Ukraine's President Volodymyr Zelensky stated, "the accumulation of forces at the border is psychological pressure from our neighbors."
Kyiv has launched its own military drills expected to mirror Russia's games, yet officials have said little about them out of apparent anxiety of escalating tensions.
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