The United States and more than two dozen allies from four continents today launch the biggest naval exercises ever in the Middle East, centred on countering the threat of anti-ship mines.
The US insists its military muscle-flexing in "international waters" is defensive in nature and not related to a specific threat from any country.
But the war games are clearly a robust if implicit message to Iran that Washington will not tolerate any attempt to close the Strait of Hormuz, the jugular vein for global oil exports.
Iran has threatened to block the narrow waterway at the mouth of the Arabian Gulf if its nuclear facilities are attacked by Israel or the US, a move that would send global oil prices soaring.
The exercises are also designed to reassure the US's allies in the region and beyond that Washington has the resolve, firepower and international support to keep the Strait open.
"Freedom of navigation through international waterways is critical to the international community and to the nations in the region, including Iran," Lt Greg Raelson, a spokesman for the US Navy's 5th Fleet in Bahrain, said.
The 11-day exercises will also take place in the Gulf of Oman and the Gulf of Aden.
They come as Barack Obama tries to restrain Israel, which is threatening to attack Iran unless the US president sets red lines on Tehran's nuclear programme.
Washington says there is still time for diplomacy and sanctions to work. It insisted this week that if Tehran decides to make a nuclear weapon — an ambition Iran denies — the US would have a year to act to stop it.
Despite the unprecedented scale of the war games analysts doubt they will further stoke already high tensions in the region where passions have also been inflamed by an anti-Muslim film produced in the US.
"I suspect the Americans have given quiet assurances through indirect channels that they have no intention of moving into Iranian national waters," Scott Lucas, an Iran expert at Birmingham University in England, said.
"Both sides have good reasons to avoid a conflict - they have other issues to deal with right now."
Iran's navy commander, Rear Admiral Habibollah Sayyari, said his country was closely monitoring the movement of US warships in the Arabian Gulf.
But he added they were free to operate in the channel's international waterways and would only be challenged if they entered Iran's territorial waters.
Tehran views the presence of US forces in the Arabian Gulf as a threat and boasted recently it will retaliate by stationing Iranian warships in international waters off the US coast "in the next few years".
For now, however, Iranian military commanders and politicians have chosen to scoff at the US-led exercises, insisting they will not dent Iran's regional power and warning any incursion into Iranian waters will meet a "crushing response".
Sir Richard Dalton, a British former ambassador to Tehran and associate at the Chatham House think tank in London, also doubts tensions will flare during the military drills.
"You can't rule out a display of bravado by either side to test the other side, but I think that's highly unlikely because both know the stakes are serious," he said.
"These manoeuvres by both sides are a twice-a-year feature of the calendar."
Iran's ability to block the Strait has grown in recent years because it has built mini-submarines that can place underwater mines.
Tehran is estimated to have 2,000 anti-ship mines that it can also deploy rapidly by boat, aircraft and from onshore bases.
Over the summer, the US doubled the number of its minesweepers in the Arabian Gulf to eight and deployed an amphibious dock, the USS Ponce, to serve as a floating stop-off point for helicopters, patrol ships and special forces.
The aircraft carrier USS John C Stennis was also recently deployed several months ahead of schedule to ensure that two carrier strike groups are constantly in the area.
Four British minesweeping vessels will take part in the exercises.
France, Japan, Jordan and New Zealand will also be involved. The UAE is not among the confirmed participants.
Re-opening the Strait in the event of an Iranian attack could take the US and its allies five to 10 days, defence experts said.
Even a temporary disruption of tanker traffic could ignite widespread economic turmoil, however. But US military commanders say the final outcome of any clash is not in doubt: a massive retaliation that would devastate Iran's military.