Ukrainian officials say a Russian airstrike has killed at least three people in the city of Lysychansk in the eastern region of Luhansk.

Ukraine's public broadcaster on Friday quoted Luhansk Governor Serhiy Haidai as saying that the attack on Lysychansk, adjacent to the fiercest battleground of Severodonetsk, also left multiple people wounded.

Haidai said in a social media post that Russians are continuing attacks on key infrastructure, and had destroyed a highway that connects Lysychansk with a nearby city.

The New York Times newspaper reported on Thursday that many victims of Russian attacks are buried in a mass grave in Lysychansk.

It says the bodies belonged to solders as well as civilians who were killed by shelling of cities, including Lysychansk and Severodonetsk.

One Ukrainian soldier is quoted as saying that the army has been burying people since April and there are now around 300 bodies in the grave.

Russian President Vladimir Putin addressed an international economic forum in St. Petersburg on Friday, saying the Russians will achieve all the goals of what he calls the special military operation.

He also referred to a recommendation by the European Commission, the executive arm of the European Union, that Ukraine become a candidate for EU membership.

Putin said he did not oppose the move because unlike the North Atlantic Treaty Organization, the EU is not a military bloc.