LONDON,: A leading separatist military leader in east Ukraine, Igor Strelkov, has resigned, the separatists’ self-proclaimed Donetsk Republic said on its website.

It said Vladimir Kononov would replace Strelkov as the new military commander.

Strelkov’s resignation was a third change at top of the rebel leadership of the past week.

Meanwhile, a Ukrainian security spokesman said on Thursday that government forces have taken control of an eastern town, allowing them to block a Russian aid convoy from going to the rebel-held city of Luhansk.

Andriy Lysenko said the army captured Novosvitlivka on Thursday, which lies just south of Luhansk. The city has come under sustained attack from government forces for weeks and has been cut off from water and power supplies.

Moscow has sent around 260 trucks with what it says are tons of aid for Luhansk. The trucks are currently parked just short of the Ukrainian border.

Ukraine says it will not allow the Russian aid convoy into the country without oversight from the international Red Cross. Ukraine suspects the convoy could be a cover for a Russian military invasion.

In a diplomatic game of chicken, a large Russian aid convoy rolled toward the Ukrainian border on Thursday — but it was heading toward a crossing controlled by pro-Russian rebels instead of a government post as Ukraine had demanded.

Ukraine’s government threatened to block the convoy if the cargo could not be inspected and announced it was organizing its own aid shipment to the war-wracked separatist region of Luhansk.

The Russian convoy of more than 200 vehicles had been parked at a military depot in the southern Russian city of Voronezh since late Tuesday amid disagreement over how and where the aid could be delivered to eastern Ukraine, where government troops are battling armed separatists.

But on Thursday, the white-tarped trucks, some flying the red flag of Moscow and accompanied by military vehicles, drove down a winding highway through sunflower fields and green hills then turned west toward the rebel-held border crossing of Izvaryne.