The Pentagon has criticized the behavior of Iran's navy, saying it was "unsafe and unprofessional," after two separate incidents in the Strait of Hormuz last week.
A Pentagon spokesman said on March 6 that an Iranian frigate came within 150 meters of the lightly armed USNS Invincible on March 2. Then on March 4, several small assault craft came within 350 meters of the Invincible and three British naval ships.
Pentagon spokesman Navy Captain Jeff Davis said that, in both cases, the U.S. ship had to change course to avoid a collision due to "a combination of unsafe or unprofessional behavior" by the Iranian Navy.
"It's concerning because it can result in a miscalculation or an accidental provocation that we don't want," Davis said, "We actually had seen quite an improvement in Iran's behavior until recently."
Such encounters between U.S. and Iranian ships have occurred several times a year in the Persian Gulf.
The last serious incident was in January, when a U.S. Navy destroyer fired three warning shots at Iranian fast-attack vessels.
When he was campaigning, U.S. President Donald Trump vowed to "shoot out of the water" any Iranian vessels that harassed U.S. Navy ships.