The Iraqi army is struggling to hold its ground in the fight against Islamic State militants, prompting the U.S. for the first time this year to airdrop bundles of food and ammunition for Iraqi units under siege at their nation’s largest oil refinery in Bayji.

U.S. aircraft on Saturday dropped 36 containers with 16,000 pounds of ammunition, about 2,000 gallons of water and more than 7,000 field ration meals for Iraqi army units that are holding the refinery but are completely surrounded by militants loyal to the Islamic State, according to U.S. Central Command officials.

A battle for Bayji’s oil refinery has raged since June when the militants seized parts of the nearby town south of Mosul along the Tigris River in Saladin Province. Control of the facility would give the militants a potentially large revenue stream in gasoline production. […]