WASHINGTON, April 13 (AP) - Western weaponry pouring into Ukraine helped blunt Russia’s initial offensive and seems certain to play a central role in the approaching, potentially decisive, battle for Ukraine’s contested Donbas region. Yet the Russian military is making little headway halting what has become a historic arms express.

The U.S. numbers alone are mounting: more than 12,000 weapons designed to defeat armored vehicles, some 1,400 shoulder-fired Stinger missiles to shoot down aircraft, and more than 50 million rounds of ammunition, among many other things. Dozens of other nations are adding to the totals.

The Biden administration is preparing yet another, more diverse, package of military support possibly totaling $750 million to be announced in coming days, a senior U.S. defense official said Tuesday. The official spoke on condition of anonymity to discuss plans not yet publicly announced. The additional aid is a sign that the administration intends to continue expanding its support for Ukraine’s war effort.

These armaments have helped an under-gunned Ukrainian military defy predictions that it would be quickly overrun by Russia. They explain in part why Vladimir Putin’s army gave up, at least for now, its attempt to capture Kyiv, the capital, and has narrowed its focus to battling for eastern and southern Ukraine.