A shoot-out at a checkpoint set up by pro-Russian separatists in eastern Ukraine has left three people dead and others hospitalised with gunshot wounds, the Interior Ministry has confirmed.
It was not immediately clear who was responsible for Sunday's attack.
In a statement, the Interior Ministry said the shooting had taken place near a roadblock set up by a group called the People's Republic of Donetsk close to the village of Bylbasivka.
"At 2:20 [local time] unknown men in four cars arrived to the roadblock and opened fire at the people who were watching on duty. There was fire shot in response. Three persons were fatally shot and three persons were wounded," the statement said.
The unknown attackers, a group of about 12 men, left the scene taking the dead and wounded with them, it continued.
Sunday's armed clash appears to be the first since an international agreement was reached last week in Geneva to ease tensions in eastern Ukraine, where pro-Russian supporters have seized government buildings in at least 10 cities.
It throws into question an already tentative truce that was supposed to be taking place over the Easter weekend.
Russia questioned Ukraine's commitment to the deal thrashed out in Geneva last week, as Russian separatists said gunmen from Ukraine's Right Sector nationalist group had attacked them.
The Right Sector denied any role, saying Russian special forces were behind the clash.
"The Easter truce has been violated," the Russian foreign ministry said in a statement. "This provocation... testifies to the lack of will on the part of the Kiev authorities to rein in and disarm nationalists and extremists."
Right Sector spokesman Artem Skoropadsky said it was a "blasphemous provocation from Russia: Blasphemous because it took place on a holy night for Christians, on Easter night. This was clearly carried out by Russian special forces."
Al Jazeera's Jacky Rowland, reporting from Slovyansk, said the circumstances surrounding the incident were "very unclear".
"What is clear is that this incident is playing into the hands of those who do not want the Geneva agreement to succeed," she said.
Earlier, Rossiya 24 news station, a Russian channel, had reported five deaths following the clash.
It said three of the dead were with the separatists who control Slovyansk, and the other two were from a group which attacked their checkpoint, according to Reuters news agency.
Separatist gunmen maintain a firm grip over a string of towns across Ukraine's industrial east despite an international deal signed last week demanding they vacate state buildings they are occupying.
Ukrainian authorities say they have suspended military operations against the pro-Moscow rebels until after the Easter holidays, which end on Monday, in a bid to give the agreement time to stick, although Sunday's violence appears to have shattered the truce.
The self-styled mayor of the eastern Ukrainian city of Slovyansk, which is controlled by armed pro-Russian separatists, said on Sunday he has evidence proving the attackers belonged to the Ukraine's far-right group the Right Sector, including documents and foreign weapons.
Slovyansk Ponomaryov, speaking at a news conference in Slovyansk, also declared that a referendum would be held in Donetsk on May 11 to determine the region's status.
Ponomaryov called on Putin to send help to the separatists in the form of food and weapons if he could not send troops.
The pro-Russia mayor also said on Sunday he had been in contact with mediators from the Organisation for Security and Cooperation in Europe (OSCE) but did not say what had been discussed.