A large flotilla of US warships sailed through the narrowest point in the Gulf in broad daylight on Wednesday to hold drills off Iran's coast in a major show of force that unnerved oil markets.
US Navy officials said Iran was not notified of plans to sail nine ships, including two aircraft carriers, through the Straits of Hormuz, a narrow channel in international waters off Iran's coast and a major artery for global oil shipments. The manoeuvre raises pressure on the Islamic Republic, coinciding with the findings of the UN atomic watchdog that Iran had ignored Security Council demands and expanded uranium enrichment, which could lead to tougher sanctions.
Oil climbed towards $70 as the US ships sailed into the straits, through which 40 percent of globally traded oil passes. Rear Admiral Kevin Quinn, who is leading the group, said the ships would conduct exercises as part of a long-planned effort to reassure regional allies of US commitment to Gulf security.
"There's always the threat of any state or non-state actor that might decide to close one of the international straits, and the biggest one is the Straits of Hormuz," he told reporters on board the USS John C. Stennis aircraft carrier.
Tension over Tehran's nuclear ambitions has raised regional fears of a military confrontation. The US naval presence in the Gulf is the largest since the 2003 Iraq war.
Highlighting the dangers of accidental escalation, a Navy official said the Stennis had received nine enquiries from nearby countries, two from Oman and seven from Iran, including one from an Iranian vessel that sailed close by. An Iranian aircraft had also flown nearby, but was part of normal traffic.
Iran's Defence Minister Mostafa Mohammad Najjar said Tehran would resist any threat and give a "powerful answer" to enemies. Most US ships pass through the straits at night so as not to attract attention, and rarely move in such large numbers.
Navy officials said the decision to send a second aircraft carrier was made at the last minute, without giving a reason. The group of ships, carrying about 17,000 personnel and 140 aircraft scheduled to participate in the exercises that will take place over the next few weeks, crossed at roughly 0355 GMT.
The manoeuvre comes less than two weeks after US Vice President Dick Cheney, speaking aboard the Stennis during a tour of the Gulf, said Washington would stand with others to prevent Iran gaining nuclear weapons and "dominating the region".
The United States accuses Iran of trying to produce nuclear weapons, and has sought tougher UN sanctions against Iran. Iran says its nuclear ambitions are for energy purposes only.
US and Iranian ambassadors are due to meet on Monday in Baghdad to discuss security in Iraq, where the United States has accused Iran of fomenting violence. Iran denies the accusations. On the way to the straits, a public announcement called on crew to witness "some of the most powerful ships in the world", whose tight formation against a backdrop of the setting sun created a dramatic image of American naval might.
Last month, the US Fifth Fleet base in Bahrain conducted its biggest crisis response drill and in March, the US navy conducted its biggest war drills in the Gulf since 2003. Naval officials said the latest training would include air defence exercises and boarding ships posing as suspect vessels. "If the Straits of Hormuz were to be closed or there were to be some conflict there, the shipping rates would go sky high," Quinn said.