Ukraine's government launched a "large-scale operation" to retake the town of Slaviansk, the Interior Ministry said, after reports emerged that a helicopter pilot was killed in the eastern city.
Interior minister Arsen Avakov wrote on his Facebook page: "At 4.30am [the government] began the active phase of the anti-terrorist operation in Slaviansk-Kramatorsk [...] We have asked Kramatorsk residents not to take to the streets and to be careful near windows".
The clashes around Slaviansk came only hours after a May Day parade was staged in Donetsk, which ended with pro-Russian demonstrators capturing and beating riot police guarding a regional prosecutor's building.
European Union foreign ministers added 13 people to their visa ban and asset freeze list over Ukraine's crisis.
Well that’s the voting over, and no surprises so far. A ‘Yes’ vote claimed to be 89% in Donetsk, and suddenly Ukraine is no more.
Nearly 90 percent of voters in eastern Ukrainian region voted for self-rule, the head of the separatist election commission said.