The senior United States government official with responsibility for African affairs has painted an optimistic picture of the continent's economic prospects, predicting a dramatic increase in overseas trade.

Speaking at the US Africa Business Summit in Philadelphia, the Assistant-Secretary of State, Walter Kansteiner, said there was the potential for an explosion of exports to the United States.

He said trade between the United States and sub-Saharan Africa had increased by 20% in the past nine months.

He attributed the rise largely to the African Growth and Opportunity Act, a law passed in Washington last year to reduce the barriers facing imports from Africa.

But critics point out that levels of trade and investment are still low compared with other regions.

Mr Kansteiner was chosen earlier this year by the Secretary of State, Colin Powell, because of his experience in the private sector.

An enthusiastic advocate of the power of free trade, Mr Kansteiner believes that the only way for African countries to achieve real development is if businesses, rather than governments, take the lead.

Dwindling aid

"Over the years as government aid and multilateral development assistance dwindles and gets smaller and smaller and smaller, it's going to be beholden on the private sector to really take it up and they're already doing it," he said.

"Private sector investment is already far greater than developmental assistance to sub-Saharan Africa and that's the way it should be."

Many of those attending the conference, though, would like the legislation to go much further and say considerable anomalies remain.

Walter Kansteiner himself acknowledged that the conditions for American private sector involvement in Africa had become harsher since the events of 11 September.

He said doing deals in Africa was tough even at the best of times, now it was even more difficult.