The alleged invasion plans, reported by German newspaper Der Spiegel, are said to suggest specific ways that might be taken by individual Russian units and were analyzed by the Secret Service, the CIA, and the Pentagon before being delivered to President Joe Biden's government.
US Secretary of State Antony Blinken held an emergency call with Russian diplomat Sergei Lavrov to examine the crisis today, after the "extremely detailed" plans provoked concerns of war in eastern Europe.
He cautioned his Russian counterpart that further aggression from Moscow would be met with a "resolute, massive and united transatlantic response".
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Mr Blinken had said earlier today that the crisis had reached a "pivotal moment", adding that there continues to be "very troubling signs of Russian escalation", including new forces arriving close to Ukraine's borders.
However, speaking during a live broadcast this afternoon, Mr Zelensky told the US: "If you have 100 percent-certain information about a Russian invasion of Ukraine, please share it with us."
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He added that he realized "such risks do exist" and that his country remains ready to take any measure necessary and "from any border."
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Thousands of British, American, and other European citizens - including many embassy staff - have now been advised to get out of Ukraine while they still can, as they were warned there would be no military evacuation after a Russian attack.
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The first haul of visibly relieved British families arrived at UK airports today, including a medical student from Birmingham and a couple with a young daughter, who landed at Gatwick.
It comes as the Ukrainian Ministry of Defense reported seven incidents of ceasefire violations in the rebel-held Donetsk region over the past 24 hours, accusing Russian-backed forces of "opening fire" on the outskirts of Pisky.
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And tensions could aggravate starting Sunday, when a critical stage in the Russian military exercises around Ukraine begins in the Black and Azov Seas on the country's southern coast.
The maneuvers, set to last a week, will ultimately obstruct international shipping to and from the Sea of Azov as the Russian naval blockade will put a stranglehold on the narrow Kerch Strait between Russia and Crimea.
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Kremlin spokesman Dmitry Peskov has claimed the movements of Russian ships in the Black Sea are in compliance with international maritime law. Still, the potential for a full-scale amphibious attack on Ukraine has not been lost on NATO observers.
