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

U.S. Secretary of State Antony Blinken crossed the border into Ukraine Saturday after meeting with Ukrainian Foreign Minister Dmytro Kuleba at the Korczowa Border Crossing Point.

"The entire world stand with Ukraine," Blinken said, and Kuleba added that he hopes Ukrainians will see this as a "clear manifestation that we have friends who literally stand by us."

Blinken said the sanctions imposed so far against Russia are "producing very, very concrete results" and that the pressure will "grow" until this "war of choice is brought to an end."

When asked directly about helping Kuleba with more firepower, Blinken said, "the support for Ukraine not only has been unprecedented, not only is going to continue, it's going to increase."

Kuleba said Ukraine "appreciates" sanctions that have been announced in the last week, but that more economic and political pressure and "necessary weapons," would "save many lives in Ukraine... many sufferings will be avoided."

Kuleba also said that they are “satisfied" with already arranged supplies of anti-tank weapons and ammunition, but that “it’s no secret” they still want fighter jets and air defense systems.

He also thanked the U.S. for sending stingers, and said they were used on Saturday.

"Just today we shot down three Russian attack aircrafts, which were bombing our cities with the use of stingers but we need -- so to say -- big air defense systems to ensure the safety of our skies. If we lose the skies, there will be much, much more blood on the ground,"Kuleba said.

In response to questions about NATO’s refusal to impose a no-fly zone over Ukraine, Kuleba said it’s a "sign of weakness," but stayed optimistic that they will change their minds.

"The time will come," he said.

-ABC News' Conor Finnegan and Justin Gomez