WASHINGTON—The U.S. military is deploying 2,000 additional troops, three new antimissile systems, two squadrons of jet fighters and other equipment to Saudi Arabia in an accelerating U.S. buildup meant to counter Iranian hostilities in the region, U.S. defense and military officials said Friday.

The move represents the largest of three rounds of U.S. military deployments to Saudi Arabia since July, and comes as U.S. lawmakers hold a negative view of arms sales and support to Riyadh, exemplified by a bipartisan vote earlier...