Ukraine’s president pushed back Thursday on President Joe Biden’s suggestion that a “minor incursion” by Russia into Ukraine might not merit a strong international response.

“We want to remind the great powers that there are no minor incursions and small nations,” Ukrainian President Volodymyr Zelenskyy wrote in a tweet Thursday morning. “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.”

Zelenskyy’s comment was a remarkable retort from a close U.S. ally that has received millions of dollars in military assistance.

During a news conference Wednesday, Biden said the U.S. would hold Russian President Vladimir Putin accountable if Russia invades Ukraine but suggested the consequences would depend on the extent of Russia’s aggression toward its neighbor.