The United Kingdom is imposing sanctions on Belarus in response to the role the country is playing in Russia’s invasion of Ukraine, including facilitating the invasion from within its borders.

Four senior defense officials have been sanctioned, leaving them unable to travel to the U.K. and freeing any of their U.K.-based assets. Also sanctioned are a Belarusian aircraft repair plant and a military semiconductor manufacturer.

Britain's Foreign Secretary Liz Truss said, "We are inflicting economic pain on [Russian President Vladimir] Putin and those closest to him. … The [Belarusian President Alexander] Lukashenko regime actively aids and abets Russia’s illegal invasion and will be made to feel the economic consequences for its support for Putin."

ABC News' Christine Theodorou

The tower that provides the main signal to TV and radio in Kyiv has been struck by a Russian missile, leaving at least five dead, Ukrainian officials said.

Ukraine's Foreign Minister Dmytro Kuleba tweeted that the tower "is situated on the territory of Babyn Yar. On September 29-30, 1941, Nazis killed over 33 thousand Jews here. 80 years later, Russian Nazis strike this same land to exterminate Ukrainians. Evil and barbaric."

Ukraine's President President Volodymr Zelenskyy tweeted, "What is the point of saying «never again» for 80 years, if the world stays silent when a bomb drops on the same site of Babyn Yar? At least 5 killed. History repeating."

President Joe Biden and Zelenskyy discussed the attack on the TV tower that impacted the Babyn Yar Holocaust memorial on their call Tuesday, according to the White House.

-ABC News' Christine Theodorou

The Russian forces charging toward Kyiv haven't made progress in the last day as they face Ukrainian resistance and low food and gas supply, a senior U.S. defense official told reporters Tuesday.

However, it could be a deliberate pause, the official said. "Part of the stall could be ... as a result of their own self-determined sort of pause in operations -- that they are possibly regrouping, rethinking, reevaluating," the official said.

The U.S. believes Russian forces "have committed now more than 80% of what was their pre-staged combat power," the official added.

The official said some Russian soldiers weren't told they were going into combat. The official said "not all of them were apparently fully trained and prepared."

The strong Ukrainian resistance has also hurt morale, according to the official.

Russia has now launched more than 400 missiles on Ukraine, the official said. The U.S. believes Russia has launchers that could be used for thermobaric weapons, but cannot confirm their use, the official said.

Russian forces are making the most progress in the south. Russians are attacking Kherson in south Ukraine, which "appears very much to be contested city at this point," the official said.

Russians are also approaching Mariupol in southeastern Ukraine, and while they haven't yet entered the city, "they are close enough now that they could attack Mariupol with long range fires," the official said.

Two towns on the path to Mariupol are believed to be occupied by the Russians, according to the official.

The U.S. believes the Russians hope to move north out of Mariupol up to the heavily-contested city of Kharkiv. The official said they believe Russian forces are trying to encircle Kharkiv.

The U.S. official noted that they've seen "certain risk-averse behavior by the Russian military" over the last week.

"Take the amphibious assault, for instance. They put those troops ashore a good 70 kilometers away from Mariupol because they knew Mariupol was going to be defended and they could put them ashore in an uncontested environment. And they still haven't reached Mariupol," the official said.

"They are not necessarily willing to take high risks with their own aircraft and their own pilots," the official said.

"And of course we're seeing that on the ground -- the fairly slow and steady progress that they have made, and you guys are seeing it for yourselves on the ground where ... units are surrendering, sometimes without a fight."

-ABC News' Matt Seyler

A spokesperson for the U.N. High Commissioner for Human Rights said 136 civilians have been killed in Ukraine, including 13 children.

Another 400 Ukrainian civilians have been wounded, spokesperson Liz Throssell said.

Russian President Vladimir Putin warned Friday that the situation in eastern Ukraine is escalating, amid fears Moscow is seeking a pretext to attack its ex-Soviet neighbour.

"Unfortunately, right now we are seeing, on the contrary, an escalation of the Donbas situation," Putin said at a joint press conference in Moscow on Friday, following a meeting with Belarusian President Alexander Lukashenko.

Putin reiterated Russia's demand that the Ukrainian government engage in direct talks with the Russia-backed separatists in Donbas, a breakaway region of southeastern Ukraine.

"All Kyiv has to do is sit down at the negotiating table with Donbas representatives and agree on the political, military, economic and humanitarian measures to end the conflict," he said. "The sooner it happens the better.”

Russia has demanded for years that Kyiv negotiate with the separatists directly, but Ukraine has always refused because it views them as Kremlin puppets and it would legitimize Moscow's false narrative that the ongoing conflict is exclusively a civil war and does not involve Russia.

Putin also stated that the United States and other members of NATO "are not disposed to properly accept" Russia's key demands for security guarantees that Ukraine will never join NATO and that the military alliance pull its troops back from Eastern Europe. He said Moscow will not accept talking about the other proposals the U.S. has put forward without discussing these top requests.

"We are prepared to follow a negotiating track, on the condition that all aspects are considered in a package, not separately from Russia's principal proposals, whose implementation is an unconditional priority for us," he told reporters.

Putin also said he "paid no attention" to the reports in Western media of Feb. 16 being the alleged date of a possible Russian invasion of Ukraine that U.S. officials had given, calling it a "hoax."

"I honestly just didn't pay attention to it. There are plenty of hoaxes. Constantly reacting to them is more trouble than it's worth," he added. "We do whatever we see fit and will do so further down the road. Of course, we watch what is going on in the world and around us. But we have clear and comprehensible guidelines that correspond with the national interests of the people of Russia and the Russian state."

Meanwhile, Lukashenko insisted that neither Belarus or Russia want a war and blamed the current tensions on the West. He said the massive joint military exercises currently being held in Belarus with Russia are directed at reinforcing their borders due to "growing military danger," which he claimed was caused in part by Western countries "pumping Ukraine" with weapons.

"With the military danger growing on our borders and Ukraine being pumped with weapons, Belarus and Russia are forced to look for appropriate ways to repel potential attacks," Lukashenko told reporters.

But the Belarusian leader also warned that, for the first time in decades, Europe is on the edge of a conflict that could "draw in almost the entire continent."

"You see that it does not depend even on our neighbors, including Ukraine, anymore. It is also obvious to you who the exacerbation of tensions near our borders depends on," Lukashenko said. "For the first time in decades, we have ended up on the verge of a conflict, which, unfortunately, is capable of drawing in almost the entire continent, like a vortex."

"Today, we're witnessing, in all its glory, irresponsibility and, forgive my frankness, the stupidity of a number of Western politicians," he added, "and the behavior denying logic and reasonable explanations of the leaders of our neighboring states and their downright morbid desire to walk right on the edge."

-ABC News' Anastasia Bagaeva and Patrick Reevell