Ukraine is no longer low on artillery ammo because Russia abandoned so much in recent retreats

Ammunition left behind by fleeing Russian troops is filling Ukraine's depleted reserves and powering its counter-offensive, according to The Wall Street Journal.

Russia's hurried retreat from Kharkiv in early September saw soldiers abandoning a mass of hardware, including tanks, other armored vehicles and howitzers.

They also left behind huge quantities of Soviet-caliber artillery shells, the paper reported.

Much of Ukraine's military arsenal is Russian or Soviet equipment, making it hard for them to replenish stocks.

In March, western officials reported that Ukrainian troops in Mariupol were resupplying by stealing ammo from Russian soldiers.

By June, Vitaly Kim, the governor of the southern region of Mykolaiv, said "we are out of ammo," Voice of America reported.

The US depleted its own reserves of some ammunition in supplying Ukraine, with levels of 155 mm ammunition becoming "uncomfortably low," as one unnamed defense official told the WSJ in late August.

But this has begun to change since Ukraine's lightning-fast counter-offensive in September. As its soldiers recaptured huge swathes of territory in the northeastern Kharkiv region, Russians dropped their guns and abandoned tanks.