The Obama administration has expanded U.S. sanctions on Russia in the latest round of a standoff over Ukraine. Speaking at the White House, President Obama said Russia has failed to drop military support for pro-Russian separatists.

President Obama: “Given its continued provocations in Ukraine, today I have approved a new set of sanctions on some of Russia’s largest companies and financial institutions. Along with our allies, with whom I have been coordinating closely the last several days and weeks, I’ve repeatedly made it clear that Russia must halt the flow of weapons and fighters across the border into Ukraine, that Russia must urge separatists to release their hostages and support a ceasefire, that Russia needs to pursue internationally mediated talks and agree to meaningful monitors on the border.”

The new sanctions are the most extensive on Russia to date, with targets including the state-controlled energy giants Gazprom and Rosneft. Ukraine has seen continued violence in recent weeks, with the U.S.-backed Kiev government launching major attacks on Russian-leaning southeastern areas.