WASHINGTON — Charging toward an Iran nuclear agreement, President Barack Obama is assuring Arab allies that they are safe from the threat of an empowered Tehran as he seeks to shore up some of America’s most critical security partnerships. However, Obama’s claim of winning Arab support for his nuclear diplomacy appears far from certain.

The president on Thursday pledged Washington’s “ironclad commitment” to the Sunni governments of the Persian Gulf and even spoke of authorizing U.S. military force if their security is endangered by Shiite Iran or anyone else.

Obama invoked the start of a “new era of cooperation” that would last for decades to come, even as Saudi Arabia and others in the region are deeply unnerved by the prospect of an accord with Iran that would impose a decade-long freeze on its nuclear program and potentially provide it tens of billions of dollars’ worth of relief from international sanctions.