Kiev's military spokesman Andriy Lysenko said government forces came under particularly heavy fire from 122-millimetre howitzers in the rebel-controlled Lugansk province.
Lugansk's Kiev-appointed governor Gennadiy Moskal wrote on his website that two servicemen were also injured in attacks on villages near the border with Russia.
Separatist commander Eduard Basurin said three of his fighters and five civilians were also hurt in the neighbouring rebel-run region of Donetsk.
The two predominantly Russian-speaking provinces -- once the heart of Ukraine's now-shattered coal and steel industry -- have been waging a war for independence from Kiev's new pro-Western leadership since March 2014.
More From This Section
It has also exposed the Kremlin to Western charges of trying to either regained control -- or leave permanently damaged -- Russia's post-Soviet neighbour to the south west.
The Kremlin's relations with the West are now suffering a post-Cold War era low that has sunk Russia's economic performance due in part to the sanctions imposed by Ukraine's allies across the world.
But Russia's Vladimir Putin -- who rejects playing any role in the 14-month conflict -- signed on to a February truce deal with Ukrainian President Petro Poroshenko in the Belarussian capital Minsk that was co-sponsored by the leaders of Germany and France.
But several rounds of follow-on talks between the warring sides' envoys failed to put any meat on the bones of the loosely-worded Minsk plan.
Kiev and the insurgents still dispute where exactly the truce line keeping apart the two sides runs.
The separatists also want to hold quick local elections that cement their semi-autonomous status within a unified Ukraine.
But Kiev insists that no such vote can be held until Ukraine secures full control of the Russian border and "all foreign armed formations" leave the war zone by the end of the year.