President Joe Biden on Tuesday spoke with Russian President Vladimir Putin, directly raising concerns about the Russian military buildup on Ukraine's border.
Biden told Putin the U.S. would "act firmly in defense of its national interests" regarding Russian cyber intrusions and election interference, according to the White House. Biden also proposed a summit meeting in a third country "in the coming months" to discuss the full range of U.S.-Russia issues, the White House said.
The call comes amid a surge of cease-fire violations in eastern Ukraine, where Russia-baked separatists and Ukrainian forces have been locked in a conflict since Moscow's 2014 annexation of Ukraine's Crimean Peninsula.
More than 14,000 people have died in fighting in eastern Ukraine, and efforts to negotiate a political settlement have stalled.
Western and Ukrainian officials have raised concerns about increasingly frequent cease-fire violations in the conflict area. Reports of Ukraine's military casualties have been occurring daily over the past week, and rebels also have reported losses.