Who's the voice on radio in Iran standoff?

The threatening radio transmission heard at the end of a video showing apparently harassing maneuvers by Iranian patrol boats in the Strait of Hormuz last weekend may have come not from the Iranian crews, but from a locally famous heckler known among ship drivers as the "Filipino Monkey."

While the threat — "I am coming to you. You will explode in a few minutes" — was picked up during the incident, further jacking up the tension, there's no proof yet of its origin.

The United States on Thursday lodged a formal diplomatic protest with Iran over the incident Sunday in which Iranian speedboats made contact with U.S. warships in the Persian Gulf.

Adm. William Fallon, the top U.S. military commander in the Mideast, said Friday that Iran runs the risk of triggering an unintended conflict if its boats continue to harass U.S. warships in the strait.

The Navy is sensitive about small boats because of the 2000 al-Qaida attack on the USS Cole as it refueled in Yemen, which resulted in the deaths of 17 sailors.

Also on Friday, a Navy official said that the USS Whidbey Island fired warning shots at a small Iranian boat that was rapidly approaching it in the Strait of Hormuz on Dec. 19 during one of two serious encounters that month.

In another incident that month, the USS Carr sounded a warning by whistle Dec. 22 after it encountered three small Iranian craft, two of which were armed, the official said.

Since Sunday's incident was announced to the public a day later, the Navy has said it's unclear where the voice came from. In the videotape released by the Pentagon on Tuesday, the screen goes black at the end and the voice can be heard, distancing it from the scenes on the water.

"We don't know for sure where they came from," said Cmdr. Lydia Robertson, spokeswoman for Fifth Fleet in Bahrain. "It could have been a shore station."

"Based on my experience operating in that part of the world, where there is a lot of maritime activity; trying to discern [who is speaking on the radio channel] is very hard to do," Chief of Naval Operations Adm. Gary Roughead said Friday.

Indeed, the voice in the audio sounds different from the one belonging to an Iranian officer shown speaking to the cruiser Port Royal over a radio from a small open boat in the video released by Iranian authorities. Asked if U.S. officials considered whether the threats came from someone besides the Iranians when releasing the video and audio, Roughead said: "The reason there is audio superimposed over the video is it gives you a better idea of what is happening."

In recent years, American ships operating in the Middle East have had to contend with a mysterious but profane voice known as the "Filipino Monkey," likely more than one person, who listens in on ship-to-ship radio traffic and then jumps in, shouting insults and jabbering vile epithets. Navy women are said to suffer particularly degrading treatment.

Rick Hoffman, a retired captain who spent many of his 17 years in the Gulf, said he was subjected to the renegade radio talker repeatedly during the so-called "Tanker Wars" of the late 1980s when Iran and Iraq were at war.

"For 25 years there's been this mythical guy out there who, hour after hour, shouts obscenities and threats," he said. "He could be tied up pierside somewhere or he could be on the bridge of a merchant ship."

Additional information from The Associated Press