Authorities in Kyiv say pro-Russian separatists Grad fired missiles and mortars at a convoy of buses carrying refugees from the eastern Ukrainian city of Luhansk on August 18, leaving many dead, including women and children, Ukrainian military spokesman Andriy Lysenko said.

Andrei Purgin, a senior rebel leader in the self-proclaimed Donetsk People’s Republic, denied that separatists were responsible for the missile strike.

Purgin said rebel forces did not have the military capability to send Grad rockets into that territory.

A rebel news outlet had reported earlier that separatists and Ukrainian government forces were exchanging heavy artillery fire on August 18 in the area where the buses had been traveling.