Russia on Sunday threatened Ukraine with "irreversible consequences" after a man was killed by a shell fired across the border from Ukraine, describing the incident in warlike terms as aggression that must be met with a response.

Although both sides have reported cross-border shootings in the past, the incident appears to be the first time Moscow has reported fatalities on its side of the border in the three-month conflict which has killed hundreds of people in Ukraine.

Kiev called the accusation its forces had fired across the border "total nonsense" and suggested the attack could have been the work of rebels trying to provoke Moscow to intervene on their behalf. The rebels denied they were responsible.