President Sall responded by calling his country tolerant and not homophobic, though he said Senegal is not ready to decriminalize homosexuality.

Speaking about economic development, Obama said U.S. policy emphasizes partnership and trade rather than merely assistance.

President Sall said Africa needs good governance to make use of its resources.

“We have tremendous natural resources, we have a lot of human resources, we need infrastructure to accompany the development of all these resources, but all this in the context of good governance, otherwise these resources will be in vain," said President Sall.

First Lady Michelle Obama and her mother joined the president at a museum on Goree Island dedicated to the West African slave trade. Centuries ago, Africans were held captive here before being shipped off, in chains, to be slaves.

Obama said the tour here was a powerful moment that reminded him about the importance of human rights.

"I think more than anything what it reminds us of is we have to remain vigilant," he said.

Earlier, Obama's spoke of former South African President Nelson Mandela, now gravely ill in a Pretoria hospital.

The president called Mandela a hero for the world, whose legacy will last through the ages.

The Obamas leave for South Africa on Friday.