Russia-Ukraine updates: 2 US veterans who joined Ukrainian forces missing

On a Friday phone call with Swedish Prime Minister Magdalena Andersson and Finnish President Sauli Niinistö, President Joe Biden "underscored his support for NATO’s Open Door policy and for the right of Finland and Sweden to decide their own future, foreign policy, and security arrangements," according to the White House.

White House press secretary Jen Psaki said Thursday that the U.S. "would support" Finland and Sweden applying to join NATO "should they choose to apply."

Dmitry Polyanskiy, Russian deputy ambassador to the United Nations, told a British news podcast that Finland and Sweden officials "know the moment they become members of the NATO, it will imply certain mirror moves on the Russian side. … If there are NATO detachments in those territories, these territories would become a target -- or a possible target -- for a strike."

On Friday's call, Biden, Andersson and Niinistö "reiterated their shared commitment to continued coordination in support of Ukraine and the Ukrainian people affected by the war," according to the White House statement.

-ABC News' Molly Nagle

Secretary of Defense Lloyd Austin spoke to his Russian counterpart, Sergei Shoigu, for the first time since the invasion of Ukraine began, according to a statement from Pentagon press secretary John Kirby.

Austin urged for an immediate ceasefire and "emphasized the importance of maintaining lines of communication," the statement said.

-ABC News' Matt Seyler

Russian troops suffered "significant" loss while attempting to cross a river in the disputed Donbas region of war-torn eastern Ukraine, the U.K. Ministry of Defense said Friday in an intelligence update.

"Ukrainian forces successfully prevented an attempted Russian river crossing in the Donbas," the ministry said. "Images indicate that during the crossing of the Siverskyi Donets river west of Severodonetsk, Russia lost significant armoured manoeuvre elements of at least one Battalion Tactical Group as well as the deployed pontoon bridging equipment."

"Conducting river crossings in a contested environment is a highly risky manoeuvre and speaks to the pressure the Russian commanders are under to make progress in their operations in eastern Ukraine," the ministry added. "Russian forces have failed to make any significant advances despite concentrating forces in this area after withdrawing and redeploying units from the Kyiv and Chernihiv Oblasts."

On Wednesday, the Ukrainian Ministry of Defense released images purportedly showing a wrecked pontoon crossing over the Siverskyi Donets river, with a number of damaged or destroyed armored vehicles on both banks.

"Artillerymen of the 17th tank brigade of the #UAarmy have opened the holiday season for [Russian forces]," the ministry said in a post on Twitter, alongside the photos. "Some bathed in the Siverskyi Donets River, and some were burned by the May sun."

The Ukrainian Armed Forces' Strategic Communications Directorate also tweeted images of the scene, purportedly showing the smoking wreckage after artillery units and land forces "destroyed all attempts by the Russian occupiers to cross the Seversky Donets River."

Sen. Rand Paul, R-Ky., single-handedly sidelined the $40 billion emergency Ukraine aid bill until next week in an effort to force lawmakers to include funding for a new watchdog effort to police how the billions in taxpayer dollars are spent.

In a very rare moment, Senate Majority Leader Chuck Schumer and Senate Minority Leader Mitch McConnell joined forces.

"There is now only one thing holding us back: the junior Senator from Kentucky is preventing swift passage of Ukraine aid because he wants to add -- at the last minute -- his own changes directly into the bill. His change is strongly opposed by many members from both parties," Schumer said Thursday. "He is not even asking for an amendment … he is simply saying, 'my way or the highway.'"

But Paul stood his ground, highlighting the nearly $60 billion that the U.S. will have given to Ukraine if this package passes.

After Paul blocked an effort to expedite passage, Schumer reiterated that Paul will not get his desired changes without a vote and blamed Paul for slowing aid.

The aid bill has enormous bipartisan support and is expected to pass by sometime next week.

-ABC News' Trish Turner and Allie Pecorin