Ukraine's military has scrambled jets to strike at rebel positions, after separatists resumed missile attacks on government forces near the frontier with Russia, according to the border guard service.
Ukrainian forces also used artillery to respond to rebel fire early on Saturday, the military said, in several areas of the country's east following a missile strike by separatists on Friday that killed at least 23 government soldiers.
Ukraine's President Petro Poroshenko had promised to "find and destroy" the pro-Russian rebels responsible for the missile attack at Zelenopillya, which also wounded nearly 100.
At least two more Ukrainian soldiers were killed and about 20 injured on Saturday in a mortar bomb and missile bombardment by the rebels of army checkpoints at Dyakove and Nyzhnoderevechka near Luhansk, the government said.
Rebel fighters said Ukrainian jets had carried out raids on Saturday in the eastern town of Horlivka.
"There were a series of powerful explosions. Details are being clarified," a separatist representative, Konstantin Knyrik, was quoted as saying by Russia's interfax news agency.
The EU meanwhile said it was extending sanctions to cover 11 leaders of the pro-Moscow rebellion in eastern Ukraine.
The names published on Saturday in the EU's Official Journal include Alexander Borodai, the prime minister of the separatist Donetsk People's Republic, and his counterpart in the Luhansk People's Republic, Marat Bashirov.
The latest assets freeze and travel bans brought the total number of people affected by the EU's Ukraine-related sanctions to 72, as well as two companies whose EU-based assets have been ordered frozen.
Also on the new list were two men identified as rebel military leaders: Nikolai Kozitsyn, commander of Cossack forces, and Alexei Mosgovy, responsible for military training.
The EU Official Journal said the sanctions, agreed by EU ambassadors on Wednesday, go into effect Saturday.