Google on Tuesday said it had blocked RT and Sputnik, Russian state-linked channels, from YouTube in Europe.

“Our teams continue to monitor the situation around the clock to take swift action,” the company said.

-ABC News’ Zunaira Zaki

Ukrainian President Volodymyr Zelenskyy on Tuesday said the Russian attack on Kharkiv’s main square was an act of “undisguised terror.”

"After that, Russia is a terrorist state. No one will forgive. Nobody will forget," he said on Facebook.

-ABC News’ Clark Bentson

At least 660,000 people have fled Ukraine into neighboring countries in the six days since the Russian invasion began, the U.N. Refugees Agency said.

At the Polish border, UNHCR staff reported queues that were miles long.

“Those who crossed the border said that they had been waiting up to 60 hours,” the agency said on Tuesday. “Most arrivals are women and children from all parts of Ukraine. Temperatures are freezing and many have reported spending days on the road waiting to cross.”

Agency staff said people were waiting up to 20 hours to enter Romania. In Hungary, arrivals were “steady and waiting times vary.” The 37-mile trip between Odessa, Ukraine, and the border with Moldova was taking some refugees 24 hours, the agency said. And arrivals in Slovakia, where asylum laws were rapidly changed, were lower than elsewhere, agency staff said.

An unknown number of Ukrainian citizens have also been displaced within the country, Filippo Grandi, the agency’s commissioner, told the U.N. Security Council on Tuesday.

“The situation is moving so quickly, and the levels of risk are so high by now, that it is impossible for humanitarians to distribute systematically the aid, the help that Ukrainians desperately need,” he said.

The International Organisation for Migration said more than 470,000 people of various nationalities, “including a large number of overseas students and labour migrants,” are still in Ukraine.

-ABC News’ Zoe Magee

Russia on Tuesday launched a major bombardment of Ukraine’s second-largest city, Kharkiv, hitting a central square and its civilian administration building.

Video from the scene shows a large projective hitting next to the regional state administration building on Kharkiv’s Freedom Square, causing a huge blast. Aftermath shot on phones from the scene and inside the building, show it shattered with debris strewn around.

Ukraine’s emergency services ministry said at least six people, including one child were injured. It was unclear if anyone was killed.

Kharkiv Mayor Oleg Sinegubov confirmed the strike, calling it a “war crime.”

Monday’s shelling followed a sustained bombardment of civilian areas yesterday and overnight in Kharkiv by Russian heavy artillery, including multiple rocket launchers and an alleged use of cluster munitions.

“What is happening in Kharkiv is a war crime!” Sinegubov wrote on Facebook. “The Russian enemy is shelling whole residential neighborhoods of Kharkiv, where there is no critical infrastructure, no Ukrainian armed forces positions, which the Russians could be targeting.”

Sinegubov accused Russia of conducting the attacks during the day, when civilians were on the street. He said the city’s emergency services are unable to keep up with the number of attacks and injured.

So far at least 11 are dead, with dozens injured, he said.

Russian forces in Kharkiv appear to have shifted tactics to employing heavy artillery indiscriminately against the city, in an apparent effort to bombard and terrorize it into submission.

Sinegubov claimed the Russians were changing tactics because their offensive capabilities on the ground were running out and so they had nothing left but to launch aerial bombardments.

-ABC News’ Patrick Reevell

Secretary of State Antony Blinken closed his remarks to the U.N. Security Council meeting by challenging the Russian Federation to "announce today -- with no qualification of equivocation or deflection -- that Russia will not invade Ukraine, stated clearly stated plainly, to the world."

"And then demonstrate it by sending your troops, your tanks, your planes back to their various can hangars and sending your diplomats to the negotiating table," he added.

Blinken laid out how the U.S. believes Russia will attack Ukraine -- but said he would welcome being wrong and for Russia to withdraw.

"Now, I'm mindful that some have called into question our information, recalling previous instances where intelligence ultimately did not bear out," he said, apparently referring to a similar address then-Secretary of State Colin Powell famously made to the Security Council presenting U.S. intelligence to justify the Iraq War. "But let me be clear, I am here today not to start a war, but to prevent one," he said, citing allies that agree with U.S. assessments.

"If Russia doesn't invade Ukraine, then we will be relieved that Russia changed course and proved our predictions wrong. That would be a far better outcome in the course we're currently on. And we'll gladly accept any criticism that anyone directs at us," Blinken said.

He continued, "Russia can still make if there's any truth to his claim that is committed to diplomacy. Diplomacy is the only responsible way to resolve this crisis"

Blinken also said that he sent a letter to Russia's Foreign Minister Sergei Lavrov earlier Thursday proposing that they meet next week in Europe following their talks in recent weeks "to discuss the steps that we can take to resolve this crisis without conflict" and that U.S. is also proposing meetings at the NATO Russia Council and the OSC Permanent Council.

"These meetings can pave the way for a summit with key leaders in the context of de-escalation to reach understandings on our mutual security concerns," he added.