A top Ukrainian source tells Newsmax that Russia was advised of President Joe Biden's trip to Ukraine in advance, with the U.S. warning the Kremlin in blunt terms that they would face a harsh response if the President was put in harm's way.

While President Vladimir Putin did not make any direct move against Biden during the trip, Ukraine's military intelligence agency claimed on Sunday that Russia was staging "large-scale nuclear exercises" this week, including test launching nuclear capable missiles from both sea and land.

The Ukrainians also said a Russian nuclear-armed submarine was put on "highest level" as heavy strategic bombers were moved to forward positions at an air base in Tambov, Russia.

Newsmax CEO Christopher Ruddy broke the news of Biden's arrival in Kyiv, posting a statement on Twitter at 3:12 a.m. ET Monday reporting, "Biden just arrived in Kyiv."

He followed with another Tweet at 3:53 a.m. ET stating, "Source: "3 delegations: a delegation from Israel, the Italian PM, Biden. This crowd arranged on purpose so that nobody would think Biden was there."

Ruddy led a Newsmax team to Kyiv in May of last year and privately met with President Volodymyr Zelenskyy.

Speaking alongside Zelenskyy at Mariinsky Palace, Biden recalled the fears nearly a year ago that Russia's invasion forces might quickly take the Ukrainian capital.

"One year later, Kyiv stands," Biden said, jamming his finger for emphasis on the podium decorated with the U.S. and Ukrainian flags. "And Ukraine stands. Democracy stands. The Americans stand with you, and the world stands with you."

Biden promised new military aid for Ukraine worth $500 million during the visit.

The Associated Press contributed to this story.

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