'Undisguised Terror': Russia Puts Ukraine's Capital 'in a Vice Grip' Before Major Attack, Thousands Flee

Faced with tough opposition from Ukrainian soldiers and citizens, Russia is now targeting Ukraine's civilian population and preparing for a major assault on the capital city of Kyiv.

Ukraine's leaders say the actions of Vladimir Putin against civilians are outright terrorism. Ukraine's President Volodymyr Zelensky accused Putin of "frank, undisguised terror" and war crimes.  

A senior U.S. official told ABC News that Russia's autocratic ruler has "ratcheted up his determination to carry on" - and is "going to put Ukraine in a vice grip."

A 40-mile-long Russian convoy of hundreds of Russian tanks and military vehicles is advancing slowly on Kyiv with the latest reports indicating parts of the convoy are out of gas and food.

Meanwhile, new video from northern Ukraine shows rescue teams running into burning homes after authorities say Russian missiles targeted a residential neighborhood located near a local hospital. 

And at least five people were also killed when Russian forces fired on a TV tower in Kyiv also hitting the city's main Holocaust memorial.

"Nobody will forgive. Nobody will forget," Zelensky vowed after Russia unleashed bloodshed on the central square in Kharkiv, the country's second-largest city, and the deadly bombing of that TV tower. 

Zelensky remains defiant. A Ukrainian official claims a Russian hit squad was sent to assassinate the president but says the plot was foiled.

In Russia, police have been arresting protesters opposed to Putin's invasion of Ukraine, with tightening sanctions throwing Moscow's economy into turmoil.

President Biden announced Tuesday in his State of the Union speech that he's closing U.S. airspace to all Russian flights.

"We arrived three days ago and now the skies are closed, and we cannot go back," said Russian tourist Natalia Samokhina. 

The United Nations now estimates that nearly 700,000 Ukrainians have fled across neighboring borders, most of them women and children.

Meanwhile, U.S. officials say morale among Russian troops has suffered. Videos online appear to show captured Russian soldiers saying they thought they were being deployed for training exercises, not combat. One senior Western intelligence official estimates that 5,000 Russian soldiers had been captured or killed so far.