Secretary of State Antony Blinken spoke to his Polish counterpart, Foreign Minister Zbigniew Rau, to discuss joint security and humanitarian efforts in Ukraine, specifically Russia's attacks on civilian population centers, according to the U.S. State Department.

The two met on the Polish-Ukrainian border Saturday. The phone call comes amid disagreements over sending fighter jets to Ukraine after Poland said it is willing to send the jets to a U.S. base in Germany, the Pentagon said the move could be seen by Russia as "escalatory."

"Secretary Blinken and Foreign Minister Rau discussed ongoing diplomatic efforts, including sanctions, to stop Putin’s war of aggression. The Secretary reiterated the United States’ steadfast support for Ukraine’s sovereignty and territorial integrity," the U.S. State Department said in a release.

The State Department added, "The Secretary and Foreign Minister also discussed the continued importance of providing security assistance to Ukraine."

The call comes as Vice President Harris visits Poland, and after Defense Secretary Lloyd Austin called his Polish counterpart on Wednesday.

Blinken also spoke to Ukrainian Foreign Minister Dmytro Kuleba Wednesday, ahead of his talks with Russian Foreign Minister Sergey Lavrov.

-ABC News' Conor Finnegan

Senate Minority Leader Mitch McConnell decried the Biden administration on the Senate floor Thursday over the "bizarre argument" that played out in public after the U.S. refused to accept Poland’s offer to donate MiG-29 aircrafts to Ukraine’s military resistance.

McConnell accused the Biden Administration of "contradicting themselves" and of proving incapable to coordinate assistance efforts with NATO allies.

"The world needs President Biden and his team to be leading, taking the initiative and shaping circumstances, calmly soberly, but with confidence and decisiveness," McConnell said. "They seem to be trapped in a cycle of passivity indecision self-determines."

-ABC News' Trish Turner

Russian Defense Ministry spokesperson Igor Konashenkov held another press briefing in which he accused NATO countries of committing war crimes.

Konashenkov claimed Thursday that mercenaries from the U.K. and U.S. are increasingly attacking Russian military medics who are accomplishing humanitarian missions in Ukrainian territory.

"Attacks on Russian medics and special medical vehicles by the Ukrainian nationalists and mercenaries that came earlier from the U.S., Britain and Europe to Ukraine have become more frequent over the past few days," Konashenkov said.

Konashenkov also denied reports that the Russian military had carried out a strike on a children’s hospital in Mariupol on Wednesday, dismissing reports on the matter as an "an information provocation staged by the Kyiv regime."

"The alleged airstrike that took place is a completely staged provocation in order to maintain the anti-Russian public outcry in the Western audience," he alleged.

Russian forces have destroyed nearly 3,000 military installations in Ukraine since the invasion began, Konashenkov claimed. In the last 24 hours, 68 installations, including two sites of the Ukrainian troop control system, 12 material and technical support centers and three Osa air defense missile systems, were obliterated, he said.

As part of her trip to Poland, Vice President Kamala Harris met with 7 people who fled the Russian invasion of Ukraine and some members of the U.S. embassy staff Thursday to discuss their experiences.

"I have invited in these very important people to join me for a conversation about their experiences, and also their thoughts about what we can do the United States and our allies in this region and around the world to support the many people that have been displaced through the necessity to flee Ukraine and the harm that it represents at this moment," Harris said to the group.

Harris thanked the group for meeting with her to share their experiences.

"The conversation we will have this afternoon will help inform me, the President of the United States, and the American people about what you have experienced, so that we can best support you and your family," Harris said to the group.

Before the press was ushered out, Harris sought to reassure the participants.

"We are here to support you and you are not alone. And I know there's so much about the experience that you've had that has made you feel alone. You are not alone," she pledged.

-ABC News' Molly Nagle

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