(CNN) President Joe Biden on Wednesday ruled out sending US troops to Ukraine to defend the country from a Russian invasion a day after laying out the consequences for such an incursion during a stern phone call with President Vladimir Putin.
It was Biden's first time describing Tuesday's two-hour conversation, which officials said grew tense at moments as the two men sparred over the massive build-up of 70,000 Russian troops surrounding Ukraine on three sides.
Biden ended the conversation without any further clarity on whether Putin had made up his mind to launch an invasion, officials said afterward.
But a day later, both he and Putin said new diplomatic channels could soon be opened in an attempt to provide an off-ramp to conflict.
Speaking to reporters as he departed the White House for Kansas City, Biden said he warned Putin he would impose sanctions "like none he's ever seen" should the Russian troops massed on Ukraine's border escalate into an assault.
But he said the US would not dispatch its own forces to protect Ukraine, a stance that US officials have previously ruled out as well.
"That is not on the table," he said. "We have a moral obligation and a legal obligation to our NATO allies if they were to attack under Article 5, that's a sacred obligation. That obligation does not extend to ... Ukraine."
Instead, Biden said he told Putin in direct terms that the economic consequences of an incursion would be devastating.
"I was very straightforward. There were no minced words. I was polite but I made it very clear: If, in fact, he invades Ukraine, there will be severe consequences. Severe consequences. Economic consequences like none he's ever seen or ever have been seen, in terms of being imposed," Biden said.
He said he believed his Russian counterpart received the message.
"He knows. His immediate response was he understood that," Biden said.
American officials have previewed a lengthy set of possible sanctions on Russia, including on members of Putin's inner circle and the country's energy sector, as options for Biden as he moves ahead. The President has been coordinating with allies in Europe -- whose countries are tied more closely to Russia economically -- on a joint sanctions effort.
The consequences of an invasion would go beyond sanctions, however. Biden said he told Putin he would likely have to increase US troop presence in Europe to reassure NATO allies of the United States' continued support if Russia went ahead with an invasion.
Putin has long complained about the presence of NATO troops along Russia's border, alleging they are a threat to his country's security.
Ukraine has been seeking membership in NATO for several years, but is not in the final stages of entering the defense bloc. Biden has said previously the country must first do more to scrub out corruption before joining.
In Tuesday's video call, Putin asked for legally binding language that would prevent Ukraine's ascension to NATO, a red line Biden would not agree to.
But he did agree to hear out Putin's concerns about NATO in a diplomatic format and said Wednesday those talks were likely to begin soon.
"We hope by Friday we'll be able to say, to announce to you that we're having meetings at a higher level, not just with us but with at least four major NATO allies and Russia, to discuss the future of Russia's concerns relative to NATO writ large and whether or not we can work out any accommodations when it comes to bringing down the temperature along the eastern front," he said.
Speaking during his own televised news conference on Wednesday, Putin said he and Biden agreed to continue the security discussions and said Russia would submit parameters for the talks to the United States within a week.
"We agreed that an appropriate structure will be created that will be able to professionally deal with this," Putin said during an appearance in Sochi, the Black Sea resort town from which he participated in Tuesday's video call with Biden.
"The conversation was very open, substantive and constructive. I hope that this is how the American side assesses the results as well. We have the opportunity to continue the dialogue, and I think this is the most important thing," he said.
This story has been updated with additional reporting.