The US government published commercial satellite images it says show Russian heavy weapons deployed near a strategic village in eastern Ukraine, ABC News reported.
"We are confident these are Russian military, not separatist, systems," the US Ambassador to Ukraine Geoff Pyatt wrote on Twitter today.
Pyatt said those systems included surface to air missiles, artillery, and rockets.
He also accused Russian military units "along the border" of "preparing a large shipment of supplies" to the Russian-backed separatist fighters.
The fresh accusations come as the clock ticks down a midnight ceasefire agreed to on Thursday as part of what aims to be a broader deal to end the nearly year-long conflict that has left more than 5,000 people dead and more than a million displaced.