Russians advances on Ukrainian cities

For Ukrainian gun commander Oleksandr Kozachenko, the long-awaited U.S. ammunition can't come fast enough as he and his comrades struggle to hold off relentless Russian attacks.

His unit's U.S.-supplied M777 howitzer, which once hurled 100 shells a day at the encroaching enemy, is now often reduced to fewer than 10.

"It's a luxury if we can fire 30 shells."

America says it's rushing ammunition and weapons to Ukraine following the delayed approval of a $61 billion aid package by Congress last month. As of early May, though, two artillery units visited by Reuters on the eastern frontline said they were still waiting for a boost in deliveries and operating at a fraction of the rate they need to hold back the Russians.

Gunners with Kozachenko's 148th Separate Artillery Brigade and the 43rd Artillery Brigade, both in the Donetsk region, said they were desperate for more 155mm rounds for their Western cannons, which had given them an edge over Russia earlier in the war.

Resurgent Russian forces, which significantly outnumber and outgun the Ukrainian defenders, have been mounting multiple attacks across the eastern Donbas region in recent months and along the country's northeastern border last week.