Polish natural gas company PGNiG announced Tuesday they received a notice from Gazprom that deliveries will be suspended starting Wednesday, April 27.

Poland has refused to pay for gas in rubles and PGNiG says they are prepared to procure gas supplies from alternate sources; storage is currently at 80%.

“Not a problem,” Polish Prime Minister Mateusz Morawiecki said.

Gazprom sent a similar notice to Bulgaria's natural gas company Bulgargaz, according to a statement from the country's energy minister Alexander Nikolov.

Morawiecki urged other EU countries, particularly Germany, to stop relying on Russian energy before Russia itself decides to cut them off, or sets economy-crippling prices.

-ABC News' Christine Theodorou, Conor Finnegan and Tomek Rolski

Sen. Rand Paul, R-Ky., had a heated back and forth with Secretary of State Antony Blinken on Capitol Hill over the war in Ukraine.

Paul pushed Blinken on support for Ukraine’s possible membership in NATO and what he called "the reasons" for the Russian invasion.

"I'm saying that the countries that have been attacked, Georgia and Ukraine, were part of the Soviet Union since 1920s,” he said.

“That does not give Russia the right to attack them,” Blinken said, explaining that the Kremlin’s security concerns about Ukraine joining NATO were adequately weighed and attempts at diplomacy were made.

"It is abundantly clear, in President Putin's own words, that this was never about Ukraine, being potentially part of NATO, and it was always about his belief that Ukraine does not deserve to be a sovereign independent country that it must be reassumed into Russia in one form or another," Blinken said.

Paul interjected during Blinken’s answer, denying he was making the argument that Russia’s actions were justified. The senator then asked Blinken about talks between Russia and Ukraine and the potential outcomes.

“Would the U.S. would President Biden be open to accepting Ukraine as an unaligned neutral nation?” Paul asked.

“We're not going to be more Ukrainian than the Ukrainians. These are decisions for them to make," Blinken said.

-ABC News' Shannon Crawford and Connor Finnegan

The United States returned diplomats to Ukraine for the first time since the beginning of the Russian invasion with a team making a day trip across the border from Poland to meet Ukrainian Ministry of Foreign Affairs officials, the State Department confirmed on Tuesday.

"The deputy chief of mission and members of the embassy team traveled to Lviv, Ukraine, today, where they were able to continue our close collaboration with key Ukrainian partners," said State Department spokesperson Ned Price.

Price called the move a "first step" toward eventually reopening the U.S. Embassy in Kyiv.

"Today's travel was a first step ahead of more regular travel in the immediate future. And as we've said, we're accelerating preparations to resume Embassy Kyiv operations just as soon as possible," Price said. "We are constantly assessing and evaluating and reassessing the security situation with a view toward resuming those embassy operations as soon as possible."

-ABC News' Conor Finnigan

Germany plans to supply Ukraine with "Gepard" anti-aircraft tanks, the German Minister of Defense announced Tuesday on Twitter.

"We made our decisions in coordination with our allies," German Defense Minister Christine Lambrecht said earlier Tuesday during a news conference at a meeting of NATO countries hosted by the United States at Ramstein Air Base. "That is, once it was clear others will deliver certain systems, we support them in that. We deliver as well. That is our way -- Germany is not doing it alone. And if Ukraine now urgently needs such air defense systems, then we are also prepared to support them."

Lambrecht said Tuesday's gathering of NATO countries to discuss strengthening Ukraine's military both in the short and long terms was a "starting point."

"The best security strategy for Ukraine is well-trained and equipped armed forces," Lambrecht said, "Germany has been providing a very high level of support in a variety of ways since the war began."

The move from Germany comes just days after Ukrainian Deputy Prime Minister Iryna Vereshchuk told ABC News that she was disappointed in Germany for seemingly dragging its feet on sending heavy artillery, including tanks, to Ukraine and said it appeared German leaders are attempting to placate Putin.

“They don’t understand. There is no way to pacify Putin," Vereshchuk said. "It would be a huge problem for NATO if Russia has dominance over the Black Sea.”

Mariupol has not yet fallen, despite Russia's demands that Ukrainian troops defending the besieged Ukrainian port city surrender, according to Ukrainian Prime Minister Denys Shmyhal.

"There [are] still our military forces, our soldiers, so they will fight until the end," Shmyhal told ABC News' George Stephanopoulos in an exclusive interview Sunday on "This Week."

Mariupol is a strategic city for Moscow because it would allow Russian forces in the south to connect with troops in eastern Ukraine's contested Donbas region. It would also give Moscow a key port.

Although Mariupol remains under the Ukrainian government's control, Shmyhal said the city's residents are suffering.

"They have no water, no food, no heat, no electricity," he said. "They ask all of our partners to support and help stop this humanitarian catastrophe."

-ABC News' Monica Dunn