Biden said an invasion would be met by a "severe and coordinated response, economic response as discussed in details with our allies as laid out very clearly with president Putin."
He added: "But there is no doubt, let there be no doubt at all, that if Putin makes this choice, Russia will pay a heavy price."
Russia has massed tens of thousands of troops on its borders with Ukraine, and Western states fear Moscow is planning a new assault on a country it invaded in 2014. Russia denies this.
