(CNN)An Iranian Islamic Revolutionary Guard Corps ship acted "unprofessional but also provocative" while approaching the USS Mahan, an American destroyer in the Persian Gulf on Monday, according to a US official.
US destroyer forced to alter course by Iranian vessel acting 'provocative'
The official said the Iranian vessel had its weapons manned and came within approximately 1,000 yards of the US destroyer.
The Mahan attempted bridge-to-bridge communication with the Iranians but got no response.
The US destroyer then fired a flare but despite the obvious signs from the Mahan, the Iranian ship continued on its course, forcing the US ship to alter direction, the official said.
But he said despite the provocations, the Mahan did not fire any warning shots.
It isn't the first time the US and Iranian navies have seen a tense standoff in the Persian Gulf.
In January, the USS Mahan fired warning shots at Iranian vessels after they came "within 900 yards or so" of the US destroyer, according to Pentagon officials.
US Defense officials said at the time that despite radio calls, flares, bells and whistles to signal the Iranian ships to stay away, they had no effect.
Pentagon spokesman Capt. Jeff Davis said there had been 35 incidents of unsafe or unprofessional behavior by Iranian vessels in 2016, although the "vast majority" had occurred in the first half.