KIEV - Armed pro-Russian separatists ambushed a convoy of Ukrainian self-defense fighters near Ukraine's eastern city of Donetsk on Friday, two days before a presidential election, and some soldiers have been wounded, military sources said. 'They (the separatists) are using automatic weapons, snipers and grenade launchers against the battalion,' Semen Semenchenko, the commander of a pro-Ukrainian militia group called the Donbass region battalion, said on his Facebook page. Yuri Bereza, the commander of pro-Ukrainian self-defense forces in a nearby region who had headed to the scene, told Reuters by telephone: 'The fighting is still going on, we are evacuating the wounded.' He gave no figure for the wounded. On Thursday, at least 13 Ukrainian servicemen were killed in a firefight with rebel gunmen south of Donetsk, an industrial hub where the separatists have proclaimed a 'people's republic' and have vowed to disrupt Sunday's presidential election.