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 intoIran 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.”