US Vice President Joe Biden said Thursday that any Russian force advances beyond Ukraine's border would constitute an invasion, for which Moscow would "pay a heavy price."

The latest White House effort was to clarify Biden's remarks a day earlier. He hinted that Russia's "minor incursion" into Ukrainian territory might prompt a more measured response from the US and its allies.

Faced with an onslaught of criticism from Republican lawmakers and Ukrainian officials that Biden's remarks had invited Russian President Vladimir Putin to take limited military action, Biden sought to clarify his comments at the outset of a White House meeting focused on domestic affairs.

"I have been unequivocal with President Putin," Biden stated. "He is clear: Any, any assembled Russian units crossing the Ukrainian border constitutes an invasion," Biden said, adding that an invasion would be responded with a "severe and coordinated economic response."

His remarks came as US Secretary of State Antony Blinken prepared to meet with Russian Foreign Minister Sergey Lavrov in Geneva on Friday in a high-stakes effort to de-escalate tensions that seemed destined to fail.

Biden stated that the US was bracing for Russia to move outside the bounds of conventional combat.

"Russia has a long history of carrying out aggression through means other than overt military action — paramilitary tactics, so-called gray zone attacks, and actions by Russian soldiers not dressed in Russian uniforms," he explained.

On Wednesday, Biden stated that he believes Moscow will invade and warned Putin that if it does, Russia will pay a "heinous price" in terms of lives lost and possible isolation from the global banking system.

However, Biden sparked alarm among friends when he stated that the response to a Russian invasion "depends on what it does."

"It's one thing if it's a minor incursion, but then we get into a fight over what to do and what not to do, and so forth," he explained.

Volodymyr Zelenskyy, Ukraine's president, was among those who expressed alarm.

"We want to warn the world's great powers that petty intrusions and little states do not exist. Similarly, there are no little casualties and minimal pain associated with the loss of loved ones," he said.

Before flying to Geneva, Blinken warned Berlin that the US and its allies would respond "swiftly and severely" if Russia launched military forces into Ukraine.

"If any Russian military forces cross the Ukrainian border and commit new acts of aggression against Ukraine, the United States and our allies and partners will respond swiftly, severely, and unitedly," Blinken said during a joint news conference with his German colleague.

Blinken later charged Russia with undermining the foundations of world order by amassing an estimated 100,000 troops near Ukraine.

In a speech in Berlin, Russia must expect a concerted and brutal global response if it invades the city that epitomized the Cold War's division of East and West.

"These are difficult issues that we are confronted with, and resolving them will take time," Blinken remarked. "I most emphatically do not believe we will resolve them in Geneva tomorrow."

He later told a Berlin-Brandenburg Academy of Sciences audience that Russia's actions toward Ukraine attempt to subvert international norms and the latest in a series of violations of Moscow's numerous treaties, agreements, and other commitments to respect other countries' sovereignty and territory.

"Perhaps no other city in the world experienced the Cold War's divisions more than this one," Blinken added. "Here, President John F. Kennedy proclaimed all free people to be Berlin citizens. President Reagan encouraged Mr. Gorbachev to demolish the wall here. At times, it appears as though President Putin wishes to return to that age. We sincerely hope not."

Blinken previously met with senior diplomats from the United Kingdom, France, and Germany to present a united front in response to concerns that Russia is plotting an invasion of Ukraine. He had seen Ukraine's president a day earlier in Kyiv.

Blinken made a point Thursday of emphasizing the United States' unity with its allies, adding that American diplomats have spoken with more than 100 allies in recent weeks "to ensure that we are speaking and acting in unison when it comes to Russia."

"That unity gives us strength," he continued, "a strength, I might add, that Russia does not and cannot match." "It is precisely for this reason that we form voluntary alliances and partnerships in the first place. That is also why Russia acts rashly in attempting to separate us."

In Washington, the Biden administration stated Thursday that it had imposed further sanctions on four Ukrainian officials. It alleges they are part of a Russian influence campaign to establish the pretext for an invasion. Parliamentarians Taras Kozak and Oleh Voloshyn and two former government officials are named in the sanctions. According to Treasury, all four have been directly involved in disinformation attempts by Russia's federal security service, or FSB.

Russia denies planning an invasion and has accused the West of orchestrating "provocations" in Ukraine, citing recent deliveries of armaments by British military transporters.

Maria Zakharova, a spokeswoman for Russia's Foreign Ministry, claimed that Ukrainian and Western talk of an imminent Russian invasion was a "cover for staging large-scale provocations of their own, including military in nature."

Russia seeks legally obligatory security assurances, including a permanent ban on Ukraine's accession to NATO, which Kyiv desires, and eliminating the majority of the US and allied military presence in eastern Europe.

The US and its European allies have indicated that they are willing to accept certain less dramatic gestures. The Russian demands are off the table, and Putin is aware of their impossibility. This, Blinken asserted, demonstrates Putin's hidden motive.

"Our good-faith gestures have thus far been rebuffed –– because, in reality, this crisis is not primarily about weapons or military bases," he explained. "It is a matter of Ukraine's sovereignty and self-determination, as well as those of other post-Soviet states. And, at its heart, it is about Russia's rejection of a united and free Europe following the Cold War."

Russia stated on Thursday that it will conduct extensive naval operations until February, some of them in the Black Sea, involving over 140 warships and over 60 aircraft. Separately, Spain's military minister announced that the government had approved the deployment of two warships to the Black Sea.

Concerned that threats of penalties would not sway Putin, Blinken made a direct plea to the Russian people to oppose any intervention.

"You, like all people everywhere, deserve to live in security and dignity, and no one — not Ukraine, not the United States, not the NATO member states — is aiming to imperil that. However, what truly jeopardizes your security is a senseless war with your Ukrainian neighbors, with all the associated expenses — most notably for the young people who would risk or even offer their lives in the process," he warned.

The US and NATO are confronted with a difficult challenge in Ukraine. Biden has stated that he has no intention of sending combat troops in the event of a subsequent Russian invasion. However, he may pursue less spectacular but dangerous military choices, such as assisting a post-invasion Ukrainian resistance.

The justification for avoiding directly intervening in a Russia-Ukraine conflict is straightforward: The US is under no treaty duty to Ukraine, and waging war against Russia would be a huge bet. However, doing too little has risks as well.