The State Department confirmed on Friday that Russia has sent tanks and other heavy weapons to separatists in Ukraine.
A convoy of three T-64 tanks, several BM-21 "Grad" multiple rocket launchers and other military vehicles crossed the border near the Ukrainian town of Snizhne, State Department officials said. Reports and images of the weapons' presence circulated on Thursday, but there were conflicting claims about where they had come from.
"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 earlier this week about the flow of Russian arms to separatists in Ukraine in a phone call to Sergey V. Lavrov, the Russian foreign minister.
An apartment building in Slovyansk, Ukraine, showed damage Thursday from weeks of fighting.
The T-64 is an obsolescent tank no longer in active use by Russian forces, but still kept in storage in southwest Russia.
"Russia will claim these tanks were taken from Ukrainian forces, but no Ukrainian tank units have been operating in that area," the State Department said Friday afternoon. "We are confident that these tanks came from Russia."
"We also have information that Russia has accumulated multiple rocket launchers at this same deployment site in southwest Russia, and these rocket launchers also recently departed," the State Department added. "Internet video has shown what we believe to be these same rocket launchers traveling through Luhansk."
—By Michael R. Gordon for the New York Times