KIEV, Ukraine — Fierce fighting raged in eastern Ukraine on Thursday in what appeared to be a last-gasp attempt by government troops to snatch back territory from pro-Russian separatists before the arrival of a Russian aid convoy overseen by the Red Cross.

Trucks loaded with water, generators and sleeping bags for desperate civilians in the besieged city of Luhansk began moving through Ukrainian customs after being held up at the border for a week, in part because of safety concerns and Ukrainian fears that the convoy’s arrival could halt the military’s advance.

The trucks in the 200-vehicle convoy were expected to cross into Ukraine on Friday morning on their way to Luhansk, a city with a war-reduced population of 250,000 people, 12 miles from the Russian border.

At Russia’s urging, U.N. Secretary-General Ban Ki-moon called for a cease-fire during the humanitarian mission.

The Red Cross has said it needs assurances of safe passage from all sides to bring in the supplies and set up distribution points, so even without a formal cease-fire, Ukrainian government forces could be severely constrained in their movements.