“The message to Iran is, ‘Don’t even think about it,’ ” one senior Defense Department official said. “Don’t even think about closing the strait. We’ll clear the mines. Don’t even think about sending your fast boats out to harass our vessels or commercial shipping. We’ll put them on the bottom of the gulf.” Like others interviewed, the official spoke on the condition of anonymity because of the delicacy of the diplomatic and military situation.

Since late spring, stealthy F-22 and older F-15C warplanes have moved into two separate bases in the Persian Gulf to bolster the combat jets already in the region and the carrier strike groups that are on constant tours of the area. Those additional attack aircraft give the United States military greater capability against coastal missile batteries that could threaten shipping, as well as the reach to strike other targets deeper inside Iran.

And the Navy, after a crash development program, has moved a converted amphibious transport and docking ship, the Ponce, into the Persian Gulf to serve as the Pentagon’s first floating staging base for military operations or humanitarian assistance…

There is little evidence that the increased pressure is having the desired effect. Negotiations with Iran are at a stalemate, though a group of Iranian, American and European experts are expected to meet in Istanbul on Tuesday to review a recent American proposal and Iranian response.