Ukrainian President Volodymyr Zelensky pushed back on President Joe Biden’s comment that “a minor incursion” by Russia into his country could reveal a divide among trans-Atlantic allies about how to respond.

Zelensky, whose country is facing the possibility of a Russian invasion after Russian President Vladimir Putin amassed a significant military presence on the border between the two nations, said on social media on Thursday, “We want to remind the great powers that there are no minor incursions and small nations. Just as there are no minor casualties and little grief from the loss of loved ones. I say this as the President of a great power.” A day earlier, during a marathon press conference, Biden made headlines for appearing to suggest that a “minor” invasion would not result in the harsh sanctions and ramifications that the administration had previously threatened.

“It’s one thing if it’s a minor incursion, and we have to fight about what to do and not to do,” Biden said. “But if they actually do what they’re capable of doing with the force amassed on the border, it is going to be a disaster for Russia if they further invade Ukraine.”

“There are differences in NATO as to what countries are willing to do, depending on what happens, the degree to which they’re willing to go,” he added, explaining that the most severe sanctions on Russia “are gonna have a negative impact on the United States as well as a negative impact on the economies of Europe as well, [and] a devastating impact on Russia.”

White House press secretary Jen Psaki walked back the president’s remarks hours later.

“President Biden has been clear with the Russian President: If any Russian military forces move across the Ukrainian border, that’s a renewed invasion, and it will be met with a swift, severe, and united response from the United States and our allies,” she said. “President Biden also knows from long experience that the Russians have an extensive playbook of aggression short of military action, including cyberattacks and paramilitary tactics. And he affirmed today that those acts of Russian aggression will be met with a decisive, reciprocal, and united response.”

She also addressed Zelensky’s tweet during a Thursday morning appearance on Fox News.

“The president has conveyed directly to President Putin if there is the movement of any military troops across the border, that is an invasion,” she said. “If they go in, that is an invasion, and there will be severe economic consequences. I know President Zelensky knows that, we’ve conveyed it. It is also true, as President Zelensky has experienced, that there are a range of tactics the Russians use. We have been warning about some of those steps, including the spreading of misinformation out there, which has been widespread, was widespread in 2014, the use of cyber tools, and we also will be ready to respond to that as well and working in lockstep with Ukraine.”

Zelensky wasn’t the only Ukrainian official to speak out against Biden’s remarks.

Dmytro Kuleba, the country’s foreign minister, told the Wall Street Journal, “Speaking of minor and full incursions or full invasion, you cannot be half-aggressive. You’re either aggressive or you’re not aggressive.”

“We should not give Putin the slightest chance to play with quasi-aggression or small incursion operations,” he added. “This aggression was there since 2014. This is the fact.”

The possibility of an invasion has grown in recent days.

The White House has said this week that they’re concerned “Russia could at any point launch an attack on Ukraine” and that Russia could conduct a “false flag operation” to drum up a supposed action to justify a military response. Russia has demanded that NATO stay out of Ukraine and other nations formerly a part of the Soviet Union, while the U.S.’s goal is to avoid an invasion similar to 2014.

“Russia has continued to escalate its threat toward Ukraine; we’ve seen that again in just the past few days,” Secretary of State Antony Blinken said during a speech on Thursday in Germany.