U.S. Navy ships fired warning shots on five Iranian ships in the Strait of Hormuz on Sunday, officials said on Monday. The Iranian ships reportedly came "within 900 yards or so" three U.S. ships, a Pentagon spokesperson Capt. Jeff Davis told CNN. One of the U.S. ships reportedly used radio signals, flares, and whistles to warn the Iranian ships away, but did not receive any response. A U.S. helicopter reportedly dropped smoke grenades from above, while the U.S. ship fired warning shots. An Iranian ship deployed an unmanned aerial vehicle during the encounter. Davis described the incident as a "one-off" and "somewhat out of character" for Iran. The incident reportedly began with routine behavior from the Iranian ships, which followed the U.S. ships as they entered the Strait. The Iranian ships then reportedly began moving toward the U.S. vessels at a high speed, which the U.S. crews deemed to be dangerous. A similar incident occurred in August, when a U.S. patrol boat fired three warning shots on an Iranian boat that had allegedly been harassing it.