At least 30 people were killed after a truck carrying wounded rebels from Donetsk airport was attacked in Ukraine's Donetsk region, according to Russian media reports.

The incident took place as unidentified people used a grenade launcher against the vehicle which was making its way to a hospital, claiming the lives of those inside, as ITAR-TASS reports, citing a private TV channel's correspondent.

Officials from the self-proclaimed "Donetsk People's Republic" in southeastern Ukraine have confirmed these accounts, without specifying whether the perpetrators were Ukrainian troops.

The Voice of Russia even puts the death toll at 35 with 15 wounded, obviously including people from outside the truck to the victims.

Latest developments in the Donetsk region come as the country has held its early presidential elections on May 25, with billionaire Petro Poroshenko winning by a landslide in the first round.

Monday saw fierce skirmishes in the area of the Donetsk airport, while the "People's Republic" itself declared martial law following the Kiev government's decision to extend the so-called "anti-terrorist" operation against pro-Russian rebels in the region.

Ukraine's agency UNIAN quotes officials in charge of the operation as saying that fighting around the airport has come to an end, with terrorists being "annihilated" after refusing to obey orders to leave the airport.

Denis Pushilin, who heads the "Donetsk People's Republic", has meanwhile fled the rebel-held administration building in Donetsk, heading for an unknown location.