(Adds more details)

WASHINGTON, Jan 10 (Reuters) - The United States protested formally to the Iranian government on Thursday over an incident in which Iranian speedboats confronted U.S. Navy ships in the Strait of Hormuz, the State Department said.

State Department spokesman Tom Casey said a formal diplomatic note was sent via the Swiss ambassador in Tehran who acts as an interlocutor between the the U.S. and Iranian governments, which do not have diplomatic ties.

"We have in fact now prepared and given to the Swiss a diplomatic note formally protesting this incident," Casey told reporters, adding it was delivered on Thursday to the Swiss and would be passed on very quickly to the Iranians.

A State Department official said he did not expect to receive a response from the Iranian government from the note.

President George W. Bush called the incident last weekend a "provocative" act and warned of serious consequences if it happened again.

"We certainly don't want to see the Iranians taking any kinds of provocative actions or steps against our ships or any ships that are transiting what is a primary international waterway," Casey said.

The Strait of Hormuz, the most prominent potential "choke point" in the global crude oil trade, handles 17 million barrels per day of global water-borne crude oil trade, over a third of total global shipments.

The incident has further heightened tensions between Washington and Tehran, which is already at loggerheads over Iran's nuclear program as well as over allegations that Tehran is fanning violence in neighboring Iraq.

On Wednesday, the United States imposed sanctions on a general in Iran's elite Qods force for his alleged role in stoking up violence in Iraq. (Reporting by Sue Pleming, editing by Patricia Wilson

AlertNet news is provided by