Two leaders in the pro-Moscow separatist movement in Ukraine reportedly quit their posts Thursday, dealing a blow to the rebels battling the Ukraine military.

The more prominent of the two was the rebel's military leader, Igor Girkin, who goes by the name Strelkov, according to the BBC.

Reuters reported Thursday that the head of the self-proclaimed rebel government in Luhansk, Valery Bolotov, had also stepped down. Luhansk is adjacent to the rebel stronghold of Donetsk.

The prime minister of the Donetsk People's Republic quit a week ago amid heavy shelling of rebel-controlled areas by the Ukrainian military.

The developments came as a large convoy of trucks carrying what Russia says is humanitarian aid headed for eastern Ukraine, despite warnings from Ukraine's government that they would not be allowed to cross the border. Those trucks were later joined by military vehicles and helicopters, escalating the tensions in the region amid fears that Russian president Vladimir Putin is eyeing an invasion.