Biden attends NATO summit from Situation Room as Putin invades Ukraine

President Joe Biden attended an emergency NATO summit Friday morning from the White House Situation Room to coordinate next steps with Western allies as Russian President Vladimir Putin wages a full-scale invasion of Ukraine.

Biden said in an address Thursday that NATO would meet to "affirm our solidarity and to map out the next steps we will take to further strengthen all aspects of our NATO alliance."

He also announced escalated sanctions to correspond with the escalated Russian aggression, but not the full economic punishment Ukraine and others have called for and none yet on Putin himself, although he did say that option was "not a bluff. It's on the table."

"He has much larger ambitions than Ukraine," Biden warned of the Russian leader. "He wants to, in fact, reestablish the former Soviet Union. That's what this is about. And I think that his ambitions are completely contrary to the place where the rest of the world has arrived."

Pressed on why the U.S. hasn't gone further with sanctions, Biden said that some decisions must be made in unison with European allies -- signaling more sanctions may follow Friday's meeting of NATO's 30 member countries.

"The sanctions that we are proposing on all their banks have the equal consequence, maybe more consequence than SWIFT, number one. Number two, it is always an option but right now that's not the position that the rest of Europe wishes to take," Biden said, referring to an international messaging system that allows large financial institutions to send money to each other.

NATO Secretary-General Jens Stoltenberg offered public remarks to open the meeting and was scheduled to hold a news conference at its conclusion, which will be live-streamed on ABC News Live.

"Russia has shattered peace on the European continent," he began. "What we have warned against for months has come to pass, despite all our efforts to find a diplomatic solution. Moscow bears sole responsibility for the deliberate, cold-blooded and long-planned invasion."

Stoltenberg said NATO condemns Russia's aggression "in the strongest possible terms" and is calling on Russia to "immediately cease its military action."

"We stand with the brave people of Ukraine. We fully support Ukraine's sovereignty and territorial integrity, its right of self-defense, and its right to choose its own path," he added.

Following the meeting, NATO announced it has activated its NATO Response Force (NRF) because of Ukraine -- a significant development as it's the first time that that the alliance has activated the potentially 40,000 man force for "a deterrence and defence" role, according to a NATO spokesperson. 

"We are now making significant additional defensive deployments of forces to the eastern part of the Alliance," NATO said in a release.

The first unit to be deployed will likely be a French and German infantry brigade of 3,500 troops that is always on a heightened state of alert. Then other NATO countries will provide forces, including the U.S.

Biden reiterated on Thursday that U.S. troops would not be involved in the fight against Russia in Ukraine, but he did announce that he will deploy more forces to Germany, including some of the 8,500 troops in the U.S. that have been on a "heightened alert," and said he is open to sending additional troops elsewhere in Europe.

"Our forces are not going to Europe to fight in Ukraine but to defend our NATO allies and reassure those allies in the East," Biden said. "As I made crystal clear, the United States will defend every inch of NATO territory with the full force of American power."

Throughout the crisis, Biden has maintained U.S. involvement is about fulfilling a responsibility to defend NATO allies -- and democracy around the world.

"America stands up to bullies," Biden said Thursday. "We stand up for freedom. This is who we are."

ABC News' Luis Martinez contributed to this report.