WASHINGTON — The United States has quietly moved significant military reinforcements into the Persian Gulf to deter the Iranian military from any possible attempt to shut the Strait of Hormuz and to increase the number of fighter jets capable of striking deep into Iran if the standoff over its nuclear program escalates. 

The deployments are part of a long-planned effort to bolster the American military presence in the gulf region, in part to reassure Israel that in dealing with Iran, as one senior administration official put it last week, “When the president says there are other options on the table beyond negotiations, he means it.”

But at a moment that the United States and its allies are beginning to enforce a much broader embargo on Iran’s oil exports, meant to force the country to take seriously the negotiations over sharply limiting its nuclear program, the buildup carries significant risks, including that Iran’s powerful Islamic Revolutionary Guards Corps could decide to lash out against the increased presence.