Three Ukrainian soldiers were killed and 27 wounded in fresh clashes Thursday between pro-Russian separatists and government forces in the east, as the European Union announced more sanctions against separatist leaders.

The leader of the self-proclaimed “Luhansk People’s Republic,” Valery Bolotov, claimed that some 50 Ukrainian troops were killed in the fighting over Luhansk airport, which is controlled by government forces.

The figure was not immediately confirmed by Ukrainian sources.

President Petro Poroshenko said the size of the conflict zone had been halved following the takeover of the separatist strongholds of Sloviansk and Kramatorsk and a number of other cities.

The military moved into much of the north of the Donetsk region after separatist militias withdrew without a fight.

The leadership of the “Donetsk People’s Republic” warned that any attempts to attack them in Donetsk, a city of a million inhabitants, will result in unprecedented bloodshed.

Mr. Poroshenko said late Wednesday that there will be no talks with the separatists unless they disarm and release prisoners.

Meanwhile, the EU said that it had added 11 people to its blacklist of individuals that the bloc accuses of being responsible for the conflict.

Their names will be published later, but the targeted persons are mainly separatist leaders, EU diplomats said.

The EU has slapped travel bans and asset freezes on a number of Russians and Ukrainians following the annexation of Crimea in March.

But the separatists mocked the latest measure. “This won’t affect our work,” said Andrei Purgin, a leader of the Donetsk republic.

“We are not planning to travel to Europe and none of us has accounts in European banks.”