WASHINGTON (REUTERS) - A US citizen who had been caring for his partner in a Ukrainian hospital was killed by Russian fire as he waited in a bread line after briefly stepping out to buy food, his family said on Thursday (March 17).

Secretary of State Antony Blinken confirmed the death of an American, identified by his sisters as Mr Jimmy Hill and mourned as "the helper that people could find in a crisis".

One of his sisters, Ms Katya Hill, told CNN he had stayed in the hospital in Chernihiv, the site of heavy Russian bombardment during its invasion, to be alongside his Ukrainian partner as she battled multiple sclerosis.  

"As things were deteriorating in the city... my brother was the one that was going out to the store to bring back what food he could find," she told CNN.  

Another of his sisters, Ms Cheryl Hill Gordon, wrote on Facebook that her brother was waiting in a bread line with several others on Wednesday when they were gunned down by Russian forces. 

Reuters could not independently verify the circumstances leading to his death.  

Chernihiv police said an American had been killed by Russian shelling. Mr Blinken did not offer any details.

Mr Hill’s own Facebook posts gave a glimpse of the situation on the frontline as he repeatedly wrote about explosions, food shortages and intense bombing during the Russian assault.  

"Intense bombing! still alive. Limited food. Room very cold," Mr Hill said in his last Facebook post on Tuesday.

In another post on the same day, he wrote that "bombing has intensified".  

A day earlier, he had written that "each day people are killed trying to escape."

Mr Hill’s Facebook profile identified him as a teacher at universities in Kyiv and Warsaw.

He was a native of Minnesota.  

Mr Viacheslav Chaus, governor of the region centered on the front-line city of Chernihiv, said 53 civilians had been killed there in the past 24 hours. The toll could not be independently verified.

Russia denies targeting civilians in what it calls a "special operation" in Ukraine.  

Food and other basic necessities have been scarce amid Russia’s bombardment.

Mr Hill’s sister, Katya, said her brother had kept a stash of chocolates with him in the hospital.  

That allowed Mr Hill to "hand out chocolates whenever somebody was depressed, or just needed a little encouragement."