US President Barack Obama has hailed a new emerging Africa, on the last day of a summit in Washington DC with 40 African leaders.

Wednesday's talks covered security concerns and corruption - two areas the US administration says are holding back growth and investment in Africa.

US firms pledged $37bn (£33bn) in investment during the summit.

Closing the summit, Mr Obama said the leaders had held "genuine discussions" and pledged to hold another gathering.

"I'll strongly encourage my successor to carry on this work because Africans must know they will always have a strong partner in the United States of America," he said, describing the three-day summit as "an extraordinary event".

On Wednesday, the White House announced new aid to support African peacekeeping forces and new security co-operation.

Mr Obama said the nations had agreed to convene "experts" to discuss transparency and good governance on the continent.

"We find that in some cases, engaging a country that generally is a good partner but is not performing optimally when it comes to all the various categories of human rights, that we can be effective in working with them on certain areas and criticising them and trying to elicit improvements in other areas," he said.

During the three-day summit, Mr Obama discussed how the US was shifting its support for Africa away from humanitarian aid and towards equal economic partnerships.The president's 2013 Power Africa has pledged to double electricity in Sub-Saharan Africa, and US-run programmes aim to lift 50 million people out of poverty and double the number of children infected with HIV who are taking anti-retrovir

Elsewhere in Washington DC on Wednesday, First Lady Michelle Obama and former First Lady Laura Bush hosted a conference for spouses of the African leaders focused on education and health.

In an open letter in Seventeen magazine, Mrs Obama described a lack of educational opportunity for young women around the world, and urged US teenagers not to take their educational opportunities for granted.

"As you get yourself on track for higher education, I hope you'll work to give girls around the world opportunities to attend school too," she wrote.

The three-day event was the first of its kind in the US, although similar summits have been held in China and Europe.

The presidents of Liberia, Guinea and Sierra Leone cancelled their plans to attend amid an Ebola outbreak, and sent delegates instead.