Russia is massing more than 100,000 troops near the border with Ukraine, and is demanding that NATO not accept Kiev as a member.
The West threatens Moscow with new sanctions if it attacks Ukraine, while Russia denies planning any attack.
Recent years have seen sporadic shootings from both sides in rebel-held areas, but any escalation of the years-long conflict with Donbass separatists could stoke tensions between Russia and the West.
The agency’s report quoted representatives of the self-declared Luhansk People’s Republic as saying that Ukrainian forces used mortars, grenade launchers and a machine gun today.
Representatives of the Luhansk region in the Ukrainian-Russian ceasefire monitoring group were quoted by the Interfax news agency as saying: “Ukrainian armed forces have crudely violated the ceasefire regime, using heavy weapons that the Minsk agreements stipulate that they must be withdrawn.”