Tehran's military threatened to shoot down two U.S. Navy planes over the Strait of Hormuz in the latest tense encounter in the Persian Gulf.
Iranian air-defense stations warned the U.S. aircraft as they were flying in international airspace on September 10 that they were nearing Iranian airspace and "we will fire Iranian missiles" if they did not change course, U.S. 5th Fleet spokesman Commander Bill Urban said on September 13.
He said the Americans replied they were conducting routine operations in international airspace and the planes continued on their mission without further incident.
In another aggressive move, on September 13, the Islamic Revolutionary Guards Corps (IRGC) unveiled a new high-speed vessel that it said was aimed at deterring the presence of U.S. warships in the Gulf.
During the inauguration ceremony, IRGC navy chief Admiral Ali Fadavi denounced the American presence in the Gulf, calling it "a cause of insecurity and lawlessness" and said "the speedboat will add to Iran's deterrence power and will have an effect on the calculations of the enemy, particularly America."
U.S. State Department spokesman Mark Toner said the latest incidents add to more than 30 close encounters between U.S. warships and IRGC vessels in the Gulf so far this year and mark a "disturbing trend."
Toner noted that Iran has hawkish factions like the IRGC which compete for influence with more moderate leaders like President Hassan Rohani, who spearheaded last year's negotiations with world powers over a nuclear arms agreement.
"Iran, like many countries, has an internal political process that is defined by a lot of different dynamics," he said.
The Pentagon has denounced its various encounters with IRGC vessels this year as "unsafe" and "unprofessional," particularly ones that prompted Americans ship to fire warning shots and to swerve to avoid hitting Iranian vessels that got too close.
In January, the Iranian Navy briefly captured the crews of two U.S. patrol boats that had, through a series of blunders, strayed into Iranian territorial waters.
The 10 American sailors were released within 24 hours.