KYIV, Ukraine — The Ukrainian military said that a soldier was killed and another seriously wounded in artillery fire from Russia-backed separatist rebels Sunday, as hostilities rise sharply in the country’s east.

As of the reported attack, Ukraine says 27 soldiers have been killed in the east this year, more than half the number who died in all of 2020. Attacks have intensified in recent weeks and Russia has built up troops along the Ukraine border.

Russia denies Western claims that it has sent troops into eastern Ukraine to help the rebels, but officials say the army could intervene if Ukraine tries to retake the area by force. The troops buildup has raised sharp concerns in the West.

U.S. Secretary of State Antony Blinken warned Sunday that “if Russia acts recklessly, or aggressively, there will be costs, there will be consequences.”

Ukrainian forces and Russia-backed separatists have been fighting in eastern Ukraine since shortly after Moscow’s 2014 annexation of Ukraine’s Crimean Peninsula. More than 14,000 people have died in the conflict, and efforts to negotiate a political settlement have stalled.