The United States is training Gulf allies to "protect navigation" in the region's troubled waterways, as it seeks to build an alliance to contain Iran.

Washington's three-week International Maritime Exercise (IMX), which started on October 21, came after a number of commercial vessels were attacked in the Gulf from May, ratcheting up regional tensions.

Washington and other Western powers blamed the incidents on Iran, but Tehran has denied any involvement.

On Tuesday, the U.S. invited international media to see part of the IMX, the second-largest maritime exercise of its kind.

The maneuvers involve 5,000 personnel, 40 vessels and 17 aircraft from 50 countries deployed to the strategic waterway that separates Iran from the pro-U.S. Arab Gulf monarchies.

In June, the U.S. Navy alleged that a mine resembling Iranian weaponry was used in an attack on the Japanese-owned Kokuka Courageous tanker, targeted as it passed through the Gulf of Oman.

Then in July, Iranian Revolutionary Guards seized a British-flagged oil tanker, holding it for more than two months before releasing it.

"One of the biggest reasons for us being out here is to build international relations," said U.S. Navy lieutenant Jonathan Phares who was among 300 personnel from the U.S., France and the Gulf on the Cardigan Bay.

Those aboard showed off diving gear, underwater imaging kit and speed boats during a tour of the gun-metal grey vessel, while others demonstrated mine detection equipment.

Bahrain, which hosts the U.S. Navy's Fifth Fleet, joined the U.S.-led naval coalition in August. Saudi Arabia and the United Arab Emirates followed suit in September.

The United Kingdom and Australia are the main Western countries to have agreed to send warships to escort commercial shipping in the Gulf.

Animosity between Tehran and Washington and its allies has soared since the U.S. unilaterally abandoned a multinational deal on curbing Iran's nuclear program last year and reimposed heavy sanctions on the Islamic republic.

Most European states have declined to participate in the naval coalition, fearful of undermining their efforts to save the nuclear accord with Iran, which was badly weakened by the U.S. withdrawal.

(With input from agencies)