Tehran and Washington do not have formal diplomatic relations and the Swiss embassy looks after US interests in the country.

A state department official told Reuters news agency that he did not expect to receive a response to the note from the Iranian government.

Casey also insisted that the US Navy's version of the event, which it described as threatening, was correct.

Grainy video

Press TV said that the grainy five-minute, 20-second-long videotape provided by the Revolutionary Guards on Thursday showed the crew of an Iranian speedboat contacting a US vessel.

In video


-Pentagon video and audio of the confrontation

-Tom Ackerman reports on reaction to the incident

"Coalition warship number 73, this is an Iranian patrol," the Iranian commander is heard to say in English, asking for the vessel to confirm its number.
  
"This is coalition warship number 73. I am operating in international waters," an American voice replies.

The footage did not show the Iranian boats approaching the US ships, unlike a videotape released by the Pentagon on Tuesday.

In Washington, a Pentagon official told the Associated Press news agency that the video appeared to have been taken around the time of Sunday's confrontation, but that the controversial parts of the incident were edited out.

In the Pentagon video small Iranian boats are seen swarming around US warships in the Strait of Hormuz, and in a separate audio recording, a man threatens in English: "I am coming to you... You will explode after ... minutes."

US Navy Commander Lydia Robertson at the 5th Fleet headquarters in Bahrain said that the two different clips were probably "two different parts of the ship's transit through the strait".

Iran has denied that its boats threatened the US vessels, and accused Washington of fabricating its video.