(CNN) The US expects Russian troops could move into the Donbas region of Ukraine as soon as Monday evening or Tuesday eastern time, after Russian President Vladimir Putin recognized the two pro-Moscow territories as independent, a senior US official familiar with latest the intelligence tells CNN.
The US is still seeing preparations for a broader potential invasion including loading amphibious ships and equipment for airborne units.
President Joe Biden plans to impose new sanctions on trade and financing in the two territories in response to Putin's moves, the White House said Monday. In a statement, the White House said Biden would sign an executive order that would "prohibit new investment, trade, and financing by US persons to, from, or in the so-called DNR and LNR regions of Ukraine."
Putin signed decrees recognizing the Donetsk People's Republic and the Luhansk People's Republic in a ceremony carried on state television earlier Monday.
Russian troops continue preparations for an invasion of Ukraine, but diplomacy will be pursued "until the tanks roll," a senior US administration official said. "Russian troops have continued to move closer to the border," the official said, saying they see plans being laid for an invasion "at any moment."
At an urgent United Nations Security Council meeting convened Monday night at the request of Ukraine, US Ambassador to the UN Linda Thomas-Greenfield called Putin's recognition of the two territories an "attempt to create a pretext for a further invasion of Ukraine" and said his claim that Russian forces entering those regions are "peacekeepers" is "nonsense."
"We know what they really are," Thomas-Greenfield said of those forces in remarks at the last-minute meeting, which included Russia and the other member nations.
"We must meet the moment and we must not look away. History tells us that looking the other way in the face of such hostility will be a far more costly path," she said.
Thomas-Greenfield also said that Russia has taken the exact actions that the US predicted and that the US does not believe Putin will stop his actions now. The US, she said, will take further measures Tuesday to hold Russia accountable for the "clear violation of international law."
Still, the sanctions announced Monday by the White House targeting the specific regions were far from the devastating consequences to Russia that Biden and US officials have warned would be imposed if Russia invades, a sign that the more sweeping measures are being kept in the event that Moscow moves forward with military action to invade Ukrainian territory.
The US is declining to specify whether so-called "peacekeeping" forces sent from Russia into eastern Ukraine would constitute a further invasion of the country.
Instead, the official said Russian forces have been operating in the Donbas region since Moscow's first incursion into the country in 2014.
"Russian troops moving into Donbas would not itself be a new step. Russia has had forces in the Donbas region for the past eight years," the official said.
The official, speaking to reporters on the condition of anonymity, said the US would monitor Russian actions on the ground, but declined to say whether the entry of troops would trigger the large package of sanctions that have been promised.
"We will observe and assess what actions Russia actually takes and respond accordingly," the official said.
Biden's executive order will also allow the US to impose sanctions on anyone operating in those areas. And the White House said it would "soon announce additional measures related to today's blatant violation of Russia's international commitments."
"To be clear: these measures are separate from and would be in addition to the swift and severe economic measures we have been preparing in coordination with Allies and partners should Russia further invade Ukraine," White House press secretary Jen Psaki wrote in a statement.
Secretary of State Antony Blinken hinted that more action is coming and tweeted that "Kremlin recognition of the so-called 'Donetsk and Luhansk People's Republics' as 'independent' requires a swift and firm response, and we will take appropriate steps in coordination with partners."
The fact Russian troops may be operating more openly in eastern Ukraine could change US calculus, according to the official.
"There have been Russian troops in the Donbas for eight years now. And, you know, Russia has denied this. Now, Russia looks like it's going to be operating openly in in that region and we're going to be responding accordingly," the official said.
The official said the US would take additional actions to respond to Russia's recognition of the breakaway territories on Tuesday.
The US response followed a lengthy speech from Putin Monday, in which he attacked both Ukraine and the West before signing the decrees recognizing the two controversial separatist-held regions. Putin's announcement follows various Russian claims of provocations over the past several days that the US and Ukraine say are false-flag operations Moscow is using to try to manufacture justification for war.
Western officials fear that Monday's move is the precursor to a full-scale Russian invasion of Ukraine. US and other NATO countries have warned they have prepared severe sanctions in the event Moscow invades Ukraine that would go beyond the measures the White House announced on Monday.
NATO and European officials also condemned Putin's actions in statements. NATO Secretary General Jens Stoltenberg said the move "further undermines" Ukraine's sovereignty and territorial integrity.
"I condemn Russia's decision to extend recognition to the self-proclaimed 'Donetsk People's Republic' and 'Luhansk People's Republic,'" he said. "This further undermines Ukraine's sovereignty and territorial integrity, erodes efforts towards a resolution of the conflict, and violates the Minsk Agreements, to which Russia is a party."
British Prime Minister Boris Johnson said Monday that Putin's recognition of the separatist regions was an "ill omen and a very dark sign." The UK plans to announce new sanctions on Russia on Tuesday, UK Foreign Secretary Liz Truss said on Twitter.
Ukraine's President Volodymyr Zelensky delivered an address on Monday evening, after Ukraine's Foreign Minister Dmytro Kuleba requested the UN Security Council hold the urgent meeting.
Biden consulted with Zelensky on a call Monday afternoon, and he subsequently spoke with French President Emmanuel Macron and German Chancellor Olaf Scholz.
US officials have had private conversations with Zelensky about going to Lviv, a city more than 300 miles west of the capital, Kyiv, should such a step become necessary as Russia continues to escalate, according to sources familiar with the conversations.
The White House has publicly said Zelensky's whereabouts are ultimately a decision for him to make.
Blinken announced Monday evening that "for security reasons" State Department personnel in Lviv would "spend the night" in Poland.
"Our personnel will regularly return to continue their diplomatic work in Ukraine and provide emergency consular services," he said. "They will continue to support the Ukrainian people and the Ukrainian government, coordinating on diplomatic efforts."
While Putin held a national security meeting Monday ahead of his speech, Biden was conferring with top US officials at the White House. Blinken, Joint Chiefs Chairman Gen. Mark Milley and CIA Director Bill Burns arrived at the White House on Monday, which is a US holiday. Vice President Kamala Harris, who returned Sunday evening from the Munich Security Conference, was also at the White House.
Milley also spoke with his Ukrainian counterpart, Lt. Gen. Valery Zaluzhny, shortly after Putin recognized the independent regions in eastern Ukraine on Monday, according to a spokesman for the Joint Chiefs of Staff. The two last spoke last week and have been in regular communication as Russian forces have amassed on Ukraine's borders and begun moving closer.
Overnight, US officials downplayed the chances a French-proposed summit between Biden and Putin would materialize, suggesting the prospects of a Russian invasion of Ukraine made such a meeting highly unlikely. They said no work had been made on timing, format or location for such a summit.
Monday evening, the senior administration official said such a summit was unlikely following Putin's order as well as intelligence and indications on the ground that Russia is likely to take military action in Ukraine.
Speaking on American television morning shows, national security adviser Jake Sullivan warned Russia could be preparing for a conflict even more brutal than some initial estimates.
"We believe that any military operation of this size, scope and magnitude of what we believe the Russians are planning will be extremely violent. It will cost the lives of Ukrainians and Russians, civilians and military personnel alike. But we also have intelligence to suggest that there will be an even greater form of brutality because this will not simply be some conventional war between two armies: It will be a war waged by Russia on the Ukrainian people, to repress them, to crush them, to harm them," Sullivan said during a Monday appearance on NBC's "Today Show."
Sullivan said on ABC that "all signs look like President Putin and the Russians are proceeding with a plan to execute a major military invasion of Ukraine," making clear that an attack could begin at any moment and the step toward invasion was underway.
This headline and story have been updated with additional developments.