U.S. Secretary of State Antony Blinken said Saturday his visit to Poland comes at "one of the most urgent moments in the long history of friendship between our two countries."

Speaking at a joint press conference with Polish Foreign Minister Zbigniew Rau in the southeastern city of Rzeszow, Blinken said the ideals that bind Poland and the United States are "under threat in this region like never before."

"We will stand together, as we've been standing together, in support of Ukraine and against Russia's unprovoked unwarranted premeditated invasion," Blinken told reporters.

Out of the more than 1.36 million people who have been forced to flee Ukraine since Russian forces invaded on Feb. 24, over 756,000 have crossed into neighboring Poland, according to the latest figures from the United Nations High Commissioner for Refugees (UNHCR).

Blinken noted that "at this moment of crisis for millions of Ukrainians and as the security of Europe hangs in the balance," it's an "incredibly powerful reflection of Poland's values that those fleeing the war will find refuge in Poland."

He outlined U.S. funding to support the needs of Ukrainian refugees in Poland and other countries, including a $2.75 billion requested aid package and the $54 million in humanitarian assistance announced last week.

Meanwhile, Rau warned Russia that Poland would not recognize any territorial transfers taken by force. He told reporters that Russian shelling of residential areas and a nuclear power plant in Ukraine "are war crimes under international law" and should "be prosecuted with utmost determination."

The U.S. has yet to say whether Russia has engaged in war crimes in Ukraine.

-ABC News' Justin Gomez

A senior U.S. official told ABC News on Saturday that they have no doubt Russia's indiscriminate bombing of Ukraine will increase in the coming days.

When asked how long they think Ukraine can hold out, the official said Ukrainian forces as a "whole" are degrading but are strong and growing as individuals or "partisans." At least 500 "fighters" from elsewhere crossed into Ukraine on Friday to join the fight against Russia, according to the official.

-ABC News' Martha Raddatz

More than 1.36 million people have been forced to flee Ukraine since Russian forces invaded on Feb. 24, according to the latest figures from the United Nations High Commissioner for Refugees (UNHCR).

More than 756,000 of the refugees from Ukraine are in neighboring Poland, UNHCR figures show.

Russia's flagship airline Aeroflot announced Saturday that it will temporarily suspend all international flights from March 8.

In a statement on its website, the airline cited "the occurrence of additional circumstances that impede the operation of flights."

"The cancellation also applies to international destinations in the schedule of Rossiya and Aurora airlines," Aeroflot said.

The U.S. Department of Commerce announced Friday that it will restrict the export of U.S. luxury goods to Russia and Belarus, as well as "certain Russian and Belarusian oligarchs and malign actors located worldwide," as a result of their actions in Ukraine.

The Department of Commerce said it will impose restrictions on the export, reexport and transfer of luxury items including certain spirits, tobacco products, clothing items, jewelry, vehicles and antique goods.

"Putin’s war of choice in Ukraine continues to take a devastating toll on innocent civilians in Ukraine, fueling one of the worst humanitarian crises Europe has seen in decades," Secretary of Commerce Gina Raimondo said in a statement.

Raimondo added, "Putin and the oligarchs who fund him have gotten rich off of Putin’s rampant corruption and the exploitation of the Russian people. We will not allow Putin and his cronies to continue living in opulence while causing tremendous suffering throughout Eastern Europe. Today’s action takes away another source of comfort and reminds them that Russia is increasingly isolated."

-ABC News' Luke Barr