Kyiv and Lviv, Ukraine(CNN) Russian President Vladimir Putin has ordered troops into separatist-held parts of eastern Ukraine in what the Kremlin called a "peacekeeping" mission, just hours after he signed decrees recognizing the independence of the Moscow-backed regions.
It is unclear if Russian troop movements marked the beginning of an invasion of Ukraine that Western leaders have warned about for weeks. But multiple US and Western officials cautioned Monday's move could serve as the opening salvo of a larger military operation targeting the country.
US Ambassador to the UN Linda Thomas-Greenfield told an emergency meeting of the UN Security Council Monday evening that Putin's recognition of the pro-Moscow regions was an "attempt to create a pretext for a further invasion."
She said his claim that Russian forces are entering those regions as "peacekeepers" is "nonsense."
"We know what they really are," Thomas-Greenfield said.
In a fiery speech earlier Monday, Putin blasted Kyiv's growing security ties with the West, and in lengthy remarks about the history of the USSR and the formation of the Ukrainian Socialist Soviet Republic, appeared to cast doubt on Ukraine's right to self-determination.
"Ukraine has never had traditions of its own statehood," he said, calling the eastern part of the country "ancient Russian lands."
The decrees signed by Putin conveyed Moscow's official recognition over two breakaway territories in the Donbas region of eastern Ukraine -- the Donetsk People's Republic and Luhansk People's Republic (DPR and LPR). The decrees recognized them as independent states and guaranteed their security with Russian troops. The decrees said that Russian so-called peacekeeping forces would be deployed in the regions.
A senior US administration official said the speech was meant to "justify war" to the Russian people and that it amounted to "an attack on the very idea of a sovereign and independent Ukraine" using "a number of false claims" meant to justify military action.
"The human costs of a further Russian invasion and occupation will be devastating," the official said.
Ukrainian President Volodymyr Zelensky addressed the nation early Tuesday saying Russia's actions violate the country's "national integrity and sovereignty" and Ukraine's international borders will "remain as such."
"We are on our land. We are not afraid of anything and anyone. We don't owe anything to anyone, and we will not give away anything to anyone. And we are confident of this," Zelensky said in his video address.
Separatists in eastern Ukraine have long had substantial backing from the Kremlin, with the US, NATO and Ukrainian officials saying Moscow supplies them with advisory support and intelligence, and embeds its own officers in their ranks. Russia has always denied having its own troops on the ground.
Moscow has also distributed hundreds of thousands of Russian passports to people in Donbas in recent years, with Putin attempting to establish facts on the ground by naturalizing Ukrainians as Russian citizens. Kyiv and the West maintain that the region is part of Ukrainian territory, although the Ukrainian government asserts the two regions have been in effect Russian-occupied since 2014, when the conflict in eastern Ukraine began.
Russian Ambassador to the UN Vassily Nebenzia described Moscow's actions to recognize the two regions as protecting Russian-speaking people living in Donetsk and Luhansk against what he characterized as Ukrainian aggression. In a translated statement to the UN Security Council, Nebenzia said recognition of those regions did not take place "suddenly."
"It should be remembered that the DPR and the LPR declared their independence from Ukraine back in 2014. But we only recognize them now, despite the high-level of support for doing so both in the republics themselves and in Russian society from the very beginning," he said.
His Ukrainian counterpart Sergiy Kyslytsya demanded Russia cancel its recognition of the regions and return to the negotiating table, in comments made to the Security Council.
Earlier Monday, US Secretary of State Antony Blinken called Putin's decision to recognize the breakaway regions "a clear attack on Ukraine's sovereignty." US President Joe Biden then signed an executive order prohibiting new investment, trade and financing by US persons to, from, and in the "so-called Donetsk People's Republic or Luhansk People's Republic regions."
The order would also allow the US to impose sanctions on anyone operating in those areas.
French President Emmanuel Macron has requested the European Union adopt targeted sanctions on Russia, and British Prime Minister Boris Johnson said the United Kingdom will announce new sanctions on Russia Tuesday. "There will be severe economic consequences to its actions," the UK's ambassador to the UN Barbara Woodward told the Security Council Monday.
Biden said last month that "if any assembled Russian units move across Ukrainian border, that is an invasion" and would be met with a "severe and coordinated economic response."
On Monday, Putin held a highly choreographed televised meeting with his top officials, accusing Kyiv of carrying out acts of aggression.
Putin also accused the West of threats and blackmail during the previously unscheduled convening of the Russian security council that, in an unusually theatrical setting, was shown on television.
The broadcast aired hours after the White House announced that US President Joe Biden agreed "in principle" to French-brokered talks with Putin, as long as Russia does not further invade Ukraine. The Kremlin said earlier Monday that there were "no concrete plans" for a meeting.
Speaking about the possibility of talks with Biden, Putin -- who held two lengthy phone calls with Macron on Sunday -- hinted he was skeptical.
"Yesterday I spoke with the French President on two occasions, with the second call lasting until 2:00 a.m. or so. He assured me that the American position has changed somewhat. But when I asked what these changes are, he, unfortunately, could not say," Putin said.
He then referred to remarks made on Sunday by Blinken, who stressed once again that the issue of Ukraine's membership in NATO is "an issue for Ukraine and for NATO."
Assurances that Ukraine would not be admitted to NATO in the future are one of the central demands made by the Kremlin.
The increase in combative language from Putin came as tensions grow in eastern Ukraine.
Ukraine's Joint Forces Operation said it recorded 32 ceasefire violations as of 4 p.m. Monday local time, a number that was roughly in line with those over the weekend.
New satellite images showed intensified activity among Russian units close to Ukraine's north-eastern border and the Ukrainian Defense ministry said it recorded dozens of ceasefire violations on Sunday.