The Obama administration on Friday announced new sanctions on seven Ukrainian separatists and said it is "intensifying" talks with European allies to bring "scalpel sanctions" against Russia.
The action comes amid mounting concern that Russia is preparing to deliver more tanks and heavy artillery to pro-Russian insurgents.
The new sanctions will freeze any U.S.-held assets of seven top separatists within Ukraine, including leaders of the Donetsk People's Republic, a militia in the country's east.
A senior administration official said the U.S. was also engaging in "active conversation" with Europe on sanctions that would narrowly target Russia's technology, defense, and financial sectors.
Secretary of State John KerryJohn KerryEgypt’s death squads and America's deafening silence With help from US, transformative change in Iran is within reach Ellison comments on Obama criticized as 'a stupid thing to say' MORE and the White House are placing calls to members of the European Union to rally support for the additional penalties, the official said.
Those penalties are being pushed, the official said, due to "disturbing evidence" that Russia continues to arm separatists despite negotiations between Kiev and Moscow toward a peace deal.
The U.S. is confident that Russia last week sent tanks and rocket launchers across the Ukrainian border, the official said, and has evidence that additional tanks, fuel trucks, and support vehicles may be on their way.
The official noted that social media accounts portrayed "new shipments of tanks and heavy artillery across the border just in the last 24 hours," and that U.S. intelligence had confirmed that tanks had departed a deployment site in southwest Russia.
The U.S. said the shipments were particularly concerning because efforts toward a ceasefire agreement have been progressing since the inauguration of new Ukrainian President Petro Poroshenko.
Earlier Friday, Poroshenko's government unveiled the broad contours of a peace plan that would decentralize the Ukrainian government and provide amnesty for most separatist fighters in exchange for a withdrawal by the pro-Russian militants that have occupied government buildings.
The U.S. said the plan emerged out of at least eight rounds of diplomatic negotiations between Russia and Ukraine, and that Poroshenko and Russian President Vladimir Putin had spoken at least three times by phone.
Despite those efforts, "the Russians have not made any private statements nor have they publicly endorsed the peace plan," the official said.
Poroshenko had been expected to declare a ceasefire against the separatists in the coming days, but the U.S. said that Russia's decision to continue shipping tanks across the border could put that in jeopardy.