Secretary of State Antony Blinken said Wednesday that the United States had seen no evidence of a significant Russian withdrawal of its military forces from Ukraine's borders, despite Moscow's claim.
"Unfortunately there's a difference between Russia says, and what it does and what we're seeing is no meaningful pullback," he said on ABC News.
"On the contrary, we continue to see forces, especially forces that would be in the vanguard of any renewed aggression against Ukraine, continuing to be at the border, to mass at the border."
Blinken called the threat of an invasion "real" and reiterated Washington's call for Russia to de-escalate the situation.
"President Putin has put in place the capacity to act on very short notice," the top US diplomat said.
"He can pull the trigger -- he could pull it today. He could pull it tomorrow. He could pull it next week. The forces are there if he wants to renew aggression against Ukraine."
Blinken urged diplomacy to resolve the situation, but added: "We're prepared for diplomacy. We're prepared for aggression. We're prepared either way."