Russian President Vladimir Putin on Monday recognized the independence of two pro-Moscow separatist regions in eastern Ukraine and ordered troops to be deployed there for "peacekeeping" missions, a move that could pave the way for Russia to invade its neighbor.

The move drew condemnation from the United States and European countries. U.S. Secretary of State Antony Blinken slammed Putin for attacking Ukraine's sovereignty and territorial integrity, and announced a trade and investment ban on the two regions.

The punitive measures were separate from the "swift and severe economic measures" that the United States has been preparing in coordination with its allies and partners should Russia invade the former Soviet republic, officials of the U.S. administration of President Joe Biden said.

Russian President Vladimir Putin summons a meeting of Russia's security council at the Kremlin in Moscow, Russia on Feb. 21, 2022. (Anadolu Agency/Getty/Kyodo)

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"We will observe and assess what actions Russia actually takes and respond accordingly," one of the officials told reporters in response to a question regarding when the planned "severe" sanctions would be triggered.

The latest development came after a monthslong Russian military buildup near Ukraine and despite a flurry of diplomatic efforts by Western countries that have been seeking a de-escalation.

In televised remarks after a meeting of Russia's security council, Putin called Ukraine "an integral part" of Russia's history and reiterated his criticism that Western countries have "ignored" Russia's key demands to offer security guarantees to halt NATO's eastward expansion and preclude the possibility of Ukraine's membership of the 30-country military alliance.

"I deem it necessary to make a decision that should have been made a long time ago -- to immediately recognize the independence and sovereignty of the Donetsk People's Republic and the Luhansk People's Republic," Putin said.

The two self-proclaimed republics of the Donetsk and Luhansk regions, collectively known as the Donbas, are home to Russia-backed separatists who have been fighting Ukrainian forces following Russia's annexation of Crimea from Ukraine in 2014.

Earlier Monday, the separatist leaders called on Putin to recognize their republics' sovereignty. Putin also signed so-called friendship and mutual aid agreements with the entities he recognized as independent.

With more than 150,000 Russian troops massed along Ukraine's borders, pundits fear that Russia may find an excuse for military action amid a deteriorating security situation in the Donbas on the grounds that it needs to protect people there against Ukraine.

Meanwhile, questions have emerged over what would constitute an "invasion" resulting in tough sanctions on Moscow, with the U.S. administration official declining to tell reporters whether Russian troops entering the pro-Moscow territories in Ukraine would immediately fall into that category.

"The 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," he said.

Robert Menendez, a Democrat who serves as chairman of the Senate Committee on Foreign Relations, said in a statement that the Biden administration and its European allies must "not hesitate in imposing crushing sanctions" if any additional Russian troops or proxy forces cross into the Donbas.

On Sunday, the White House said that Biden had agreed in principle to hold a summit with Putin, provided Moscow did not take military action.

But the Biden administration official said Monday the U.S. government cannot commit to the meeting, with Russia "continuing to prepare for military action that could take place in the coming hours or days."

"Russia continues to escalate this crisis that it created in the first place. We'll continue to pursue diplomacy until the tanks roll, but we are under no illusions about what is likely to come next," he added.

The United States has sent troops to Europe to bolster the security of North Atlantic Treaty Organization allies and has been providing security assistance to Ukraine to help defend its territory.

But Washington has denied any intention to deploy U.S. forces in Ukraine, which is not a member of NATO although it aspires to join the alliance.

Citing security, the U.S. State Department said it will evacuate its personnel from Ukraine and they will spend the night in adjacent Poland. The United States had already moved its embassy operations in Kyiv to the western Ukraine city of Lviv amid fears of a possible imminent Russian invasion.