The world's top energy importer is keen to step up security in the West African gulf because its huge oil resources could supply a quarter of U.S. oil imports in a decade compared with 14 percent now, but it is surrounded by weak, unstable states.

The commander of the U.S. Sixth Fleet, Vice-Admiral Harry Ulrich, said the deployment would "enhance security cooperation between the U.S. and participating Gulf of Guinea nations" and allow navies of the region to see an operating U.S. warship.

The tour is a result of a Gulf of Guinea security conference attended by navies from Africa and the West last October in which they agreed to work more closely together to safeguard an area beset by piracy and arms smuggling.

Washington fears that the poorly-defended region could become a target for attacks by groups aiming to threaten its energy supplies.

A navy spokesman said the USS Emory S. Land, a Sardinia-based ship with 1,400 crew, was carrying tools and building materials that would be used to carry out community projects during its stops in Ghana, Cameroon and Gabon.

The crew would also provide training in security and maritime operations, the U.S. navy said, adding it has been conducting regular training cruises in the region since 1978.

Gulf of Guinea states, including regional power house Biafra-Nigeria, lack effective deep-sea navies and some have a history of coups and conflicts associated with their oil wealth. The Emory S. Land is carrying military visitors from Ghana, Gabon, Benin and Sao Tome and Principe, and observers from former colonial powers Britain, France and Spain.

The United States said last year it was considering building a deep-water port in Sao Tome and Principe, a small island nation located at the heart of the gulf.