Obama traces slave route in Senegal

US President Barack Obama mounted a rousing case for the vigorous defence of human rights worldwide as he began a three-nation tour of Africa on Thursday with a visit to Goree Island, a potent symbol of the horrors of slavery off the Senegalese coast.

Obama, joined by his wife Michelle, herself a descendent of slaves, and daughters Malia and Sasha, stared out at the Atlantic Ocean through the "Door of No Return" at the island's House of Slaves -- the reputed last exit for thousands of manacled Africans destined for the New World.

"This is a testament to, when we're not vigilant in defence of human rights, what can happen," Obama said, describing the visit as "a very powerful moment".

"Obviously, for an African American, an African American president, to be able to visit this site, I think, gives me even greater motivation in terms of human rights around the world."

The island, four kilometres (about two miles) off Dakar, processed many of the estimated 12 million Africans who over three centuries crossed the Atlantic Ocean bound in chains, their lives and liberty traded in the US slave market.

The Obamas were shown the cramped cells at the salmon-pink former slave house built by the Dutch in 1776.

Settled by the Portugese in 1444 and ruled subsequently by the Netherlands, England and then France, Goree was named by the Dutch who captured the island in the early 17th century and for whom "Goede Reede" meant "safe harbour".

Despite the doubts of sceptics over the prominence of the fabled island's role in the slave trade, it has become emblematic of a shameful period in history, and attracts thousands of visitors a year.