The primary Iranian propaganda organ, the Tasnim news agency, says a U.S. Navy warship was warned by an Iranian missile boat off rescuing a fishing boat in distress. 

The Navy tells a different story.

Radio Free Europe:

The U.S. Navy said the coastal patrol ship USS Tempest heard the distress call of an unidentified small boat about 140 kilometers from the Tempest's position.

It said another ship much closer to the boat in distress offered assistance, with that vessel communicating with Iranian naval forces.

"At no time was there any direct contact between the U.S. and Iranian maritime forces," U.S. Naval Forces Central Command (NAVCENT) said.

The Iranian and U.S. navies routinely have tense encounters in the Persian Gulf and its environs.

In August, an unarmed Iranian drone came close to a U.S. Navy warplane as it prepared to land on an aircraft carrier in the Persian Gulf, U.S. officials said at the time.

And in July, the U.S. Navy said that one of its helicopters fired warning flares at Iranian vessels approaching its ships in the Persian Gulf.

The Iranian version of the story doesn't hold water.  Any U.S. warship – even a coastal patrol boat – is more than a match for any Iranian vessel.  They certainly wouldn't be scared off.  The American ship no doubt allowed the Iranian vessel to rescue the craft since it was already on the scene and probably offered assistance in accordance with the law of the sea.

But the Iranians couldn't let the incident pass without embellishing what happened by claiming that the U.S. ran away when confronted by the Iranian navy.  Despite the fact that the USN could blow any Iranian ship out of the water, the Iranians have such an inferiority complex that they feel the need to tweak the lion's tail every once and a while.

Iranian patrol boats routinely encounter U.S. warships in the strait and sometimes adopt an attack posture, racing toward the U.S. ship.  Someday, they are going to go too far, and the Iranian navy will be down one patrol boat.