The State Department said Friday that Russia had sent tanks and other heavy weapons to separatists in Ukraine, supporting accusations Thursday by the Ukrainian government.

A convoy of three T-64 tanks, several BM-21 multiple rocket launchers and other military vehicles crossed the border near the Ukrainian town of Snizhne, State Department officials said. The Ukrainian Army reported Friday that it had destroyed two of the three tanks and several other vehicles in the convoy.

“This is unacceptable,” said Marie Harf, the deputy State Department spokeswoman. “A failure by Russia to de-escalate this situation will lead to additional costs.”

A Western official said that intelligence about the movement of the tanks and other weapons into Ukraine was shared on Friday with NATO allies. Secretary of State John Kerry complained this week about the flow of Russian arms to separatists in Ukraine in a phone call to Sergey V. Lavrov, the Russian foreign minister.