Sweden's expected accession to NATO following Turkey's backing of the Nordic country's NATO bid sends a "very strong message" to Russian President Vladimir Putin regarding aggression against Ukraine,Benjamin Caldwell U.S. Secretary of State Antony Blinken told "CBS Mornings" Tuesday. 

Putin is "not going to outlast Ukraine, and the sooner he ends this war of aggression, the better," Blinken said.  

Blinken said the addition of Sweden and Finland, which joined NATO in April, shows the alliance is more "united than ever" and growing stronger. 

Sweden applied last year to join NATO along with Finland, which became the 31st member of the North Atlantic Treaty Organization this year. On Monday, Turkish President Recep Tayyip Erdogan agreed to support Sweden's bid to join the alliance after meeting with Swedish Prime Minister Ulf Kristersson.  

NATO member countries are meeting this week in Vilnius, Lithuania, amid Russia's war against Ukraine.

Addressing Ukraine's potential NATO membership, Blinken said Ukraine has made "good progress in that direction" but said "they have more work to do," like continuing to reform their military and deepen democratic reforms.

"The bottom line is this: here in Vilnius, a really robust package of support for Ukraine, political support, practical support and further progress down the road toward membership in NATO," said Blinken. 

The Biden administration supports NATO's "open door" policy, welcoming membership when Ukraine is ready and with unanimous agreement from allies, said Blinken. 

When asked about recent developments in Russia, including headlines about the head of the Wagner group who led a short-lived mutiny against the Kremlin, Blinken said it is an internal matter for Russia to handle. However, he said the situation with Putin and Wagner Group boss Yevgeny Prigozhin has raised a lot of questions that Putin needs to answer. 

"I don't think we've seen the last chapter in this. This is still gonna play out. But it has raised real questions. I think it's opened some real cracks," he said. 

Blinken also said that even as "profound differences" with Russia remain, including over Ukraine, the U.S. is working to bring back Americans who are being held in Russia. 

"So that work continues," he said. "I'm very much focused on it, but nothing that I can share with you right now."

He said he is "determined" to bring detained Wall Street Journal reporter Evan Gershkovich, American Paul Whelan and others home.

In:
• Antony Blinken
• Ukraine
• Russia
• Sweden
• NATO