A soldier was killed and another seriously wounded in artillery fire from Russia-backed separatist rebels, the Ukrainian military said.
It brings the number of Ukrainian soldiers killed this year to 27, 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 build-up of troops has raised sharp concerns in the West.
The G7 foreign ministers of the UK, Canada, France, Germany, Italy, Japan, the US and the High Representative of the European Union said they are "deeply concerned by the large ongoing build-up of Russian military forces on Ukraine’s borders and in illegally-annexed Crimea".
Calling for greater military transparency from Russia and reaffirming the support of G7 toward an independent Ukraine, the statement added: "These large-scale troop movements, without prior notification, represent threatening and destabilising activities. We call on Russia to cease its provocations and to immediately de-escalate tensions in line with its international obligations".
US secretary of state Antony Blinken has warned 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.