A US State Department spokesperson said that an American citizen has been killed in Ukraine's Chernihiv due to "heavy artillery attack" from Russian forces, the media reported.
"We can confirm the death of a US citizen in Ukraine on March 17," the BBC quoted the spokesperson as saying in a statement late Thursday.
"We offer our sincerest condolences to the family on their loss. Out of respect to the family during this difficult time, we have no further comment."
The victim has been identified as James Whitney Hill, who was killed by heavy artillery attacks on unarmed civilians in the city, the BBC quoted a New York Times report as saying.
According to The New York Times, Hill travelled to Ukraine last December with his Ukrainian partner so she could be treated at a local hospital for multiple sclerosis.
In recent weeks, Hill had been writing about the deteriorating situation.
"Each day people are killed trying to escape. But bombs falling here at night. Risk either way," he wrote on Facebook.
"I only have wifi a few hours a day. We have enough food for a few days."
