President Obama and Russian President Vladimir Putin spoke by phone Friday for the first time since the U.S. stepped up sanctions against the Kremlin for escalating tensions in Ukraine.

“The president reiterated his deep concerns about Russia’s increased support for the separatists in Ukraine,” the White House said in a readout of the call. “The president reinforced his preference for a diplomatic solution to the crisis in Ukraine, and the two leaders agreed to keep open their channels of communication.”

Obama also brought up the U.S. contention that Russia violated a major arms control treaty by testing long-range missiles.

The White House description of the call did not include Putin’s response.

However, Putin told Obama that the sanctions were exacerbating the Ukrainian crisis and had damaged the U.S.-Russia relationship, according to officials in Moscow.

In recent days, the U.S. and European nations united behind sanctions against the Russian energy, arms and finance industries. The western powers attributed the heightened sanctions to Russia’s role in the downing of a passenger jet in Ukraine.

Obama is banking that the economic penalties will force Putin to change course in Ukraine. But Putin, at least thus far, insists that Western actions will have no influence on his actions.

Meanwhile, Vice President Joe Biden called Ukrainian President Petro Poroshenko on Friday to discuss additional U.S. aid for Ukraine.