The navy said the pirates were going further to avoid foreign navies, which have been patrolling the Indian Ocean and Gulf of Aden.
A statement from the Bahrain-based US Fifth Fleet said one raid took place at the southern end of the Red Sea at the end of May and ships should be cautious in that area.
"Pirates have also recently increased their number of attacks during the hours of darkness, highlighting the need for heightened vigilance of merchant mariners during both day and night time transits through the high risk areas," the US Navy said.
More than 30,000 vessels annually transit the pirate-plagued Gulf of Aden and the busy shipping lane has offered rich picking for raiders.
The gangs are currently holding 14 ships and more than 200 seamen in the region.
When first loaded, the map's focus falls on Somalia where most of the pirates are based. Use the arrow icons to scroll left towards Europe and the United States which are both playing a central role in tackling the problem.
Scroll to the right for a story about the Philippines, which supplies many of the world's mariners.
You can zoom in for more detail by using the "+" or "-" signs on the upper left hand side.
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