U2 lead singer Bono has called on leaders of developed countries to keep their promises to relieve the debt burden of the world's poorest countries.

Addressing a special session on Africa's future at the World Economic Forum (WEF) in Davos yesterday, Bono said the issue of corruption did not justify delaying debt cancellation for poor countries. The session was the highlight of yesterday's discussions, which included British prime minister Tony Blair, South African's prime minister Thabo Mbeki and Liberian prime minister Ellen Johnson Sirleaf.

"There is also proven corruption in the northern hemisphere;there's also the trade and unfairness in trade problem. This is corruption from the north," Bono said yesterday.

Tariffs on cotton, cocoa and other agricultural products were preventing African farmers from growing those crops and threatening their survival, he added. "I remember talking to a politician from Ethiopia who told me that the smartest people in his country are farmers because if they weren't smart, they'd be dead."

Speaking in his capacity as founder of Debt, Aid and Trade for Africa (Data), Bono said commitments given at the 2005 Gleneagles debt relief summit might not be honoured. "I fear for the promises we make being kept; if we fail it's corruption at the highest order."

Earlier in the day, the forum heard an impassioned plea from Brazilian president Luiz Inacio Lula da Silva for governments in rich countries to open their agricultural markets to the world's poorest nations.

Liberian premier Ellen Sirleaf said developed countries needed to go beyond trade liberalisation and quicken the pace of aid and debt relief. "Too often, the pace is too slow . . . You can commit to us huge sums of money but if that commitment doesn't turn into cash, and turn into cash very quickly, then it doesn't help us much.

"I do believe that Africa has the capacity to grow out of its own resources. It has to take primary responsibility for its own development, has to use its own resources effectively and efficiently," she added. "Once we do that, the only other constraint I see is [ to] get rid of the debt."

Mr Blair said he would strengthen his efforts to ensure commitments were met. "I think we need to recommit on aid. You know, we made certain commitments at Gleneagles, we've go to go back and make sure those commitments are delivered upon. I think that's very, very important."

"Africa is this magical, extraordinary continent and we've got to start describing it more as an adventure and as an opportunity, rather than a burden," Bono said.

Responding, Mr Mbeki said the mass media needed to do more to highlight Africa's attraction for investors. "Its not for lack of trying that you don't see this image in the media. When I tell a good story about Africa, a really good story about Africa, you can't believe how difficult it is to get it through."

The session was hosted by Irish-born chairman of Reuters international, Niall Fitzgerald.