Naval forces from more than 41 countries gathered in Bahrain -- across the Gulf from Iran -- on Monday to prepare for a massive minesweeping exercise, the US Fifth Fleet said.
The International Mine Countermeasures Exercise (IMCMEX) "is the largest exercise of its kind in the region and will exercise a wide spectrum of defensive operations designed to protect international commerce and trade; mine countermeasures, maritime security operations and maritime infrastructure protection," it said in a statement.
US Vice Admiral John Miller, head of US naval forces in the Gulf region, said the manoeuvres aim to "enhance international naval capability to preserve freedom of navigation in international waterways."
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On Monday, "participating nations began staging and staff integration" to prepare for the exercises out at sea starting next week, said the statement.
Thirty-five ships, 18 Unmanned Underwater Vehicles and more than 100 explosive ordinance disposal divers will participate in the anti-mine manoeuvres running until the end of May.
The excercise is taking place in a region which has often been the scene of tensions between Arab states of the Gulf and Iran, under Western pressure over its controversial nuclear programme.
IMCMEX took place for the first time last year at a time of Iranian threats to block the strategic Strait of Hormuz if it came under attack.
But US defence officials insisted last year that the exercise is not aimed at Iran or any one country, but is simply designed to hone counter-mine capabilities among allies and partners.