The world's seven richest nations have agreed to increase debt relief for the poorest countries by $1 billion.
The seven countries - which with Russia form the Group of Eight (G8) - will reduce the debt repayments for up to 22 African states under the Highly Indebted Poor Countries initiative.
But aid agencies said the debt relief would barely make up for the fall in commodity prices such as coffee and cotton on which many developing nations' economies are reliant.
G8 leaders gathered in the Canadian Rocky Mountain resort of Kananaskis are preparing to meet African heads of state on Thursday to discuss ways to help the poorest continent.
Proponents of the debt relief plan, led by Canada with backing from Britain and Germany, hope the beneficiaries will use the money that is not being sent to banks for investment in areas such as health care and education.
But Irish rock star and debt-relief campaigner Bob Geldof doubts that the measures will be adequate.
"After (the G8 summit in) Genoa last year, everyone said this was going to be the year for Africa, but in the last year you've seen a catastrophic failure to deal with the rhetoric," Mr Geldof told the BBC.
"It looked fairly promising up to about a month ago, but in the last two weeks it's all unravelled into this sort of meaningless conference," he added.
Poverty v terrorism
Andrew Graham, a spokesman for the Canadian chapter of the aid agency Care, said the sum was equal to just 50 days of debt repayment by developing countries.
He noted that the US Congress approved $40bn to fight terrorism three days after the 11 September attacks but that such huge sums were not forthcoming to help the world's poor.
"Poverty is killing more people everyday than terrorism," he said.
The African presidents - Algeria's Abdelaziz Bouteflika, Nigeria's Olusegun Obasanjo, Senegal's Abdoulaye Wade and South Africa's Thabo Mbeki - want to win backing for their Nepad plan which offers good governance in return for investment and development aid.
Canada's Prime Minister Jean Chretien is keen to devote new resources to Africa, but US President George W Bush does not want to be tied to one area and Japan has said it needs to concentrate its aid on the Asia-Pacific region.
Also on the first day of the two-day summit:
Canada has mounted its largest peacetime security operation for the summit, fearful of a repeat of violent protests such as those at last year's G8 meeting where a protester died.
Demonstrators, barred from the mountain retreat, chanted and banged drums in protest marches in Calgary, some 55 miles (90km) away and in a rain-drenched Canadian capital, Ottawa.
But there was little sign of trouble apart from traffic jams and angry commuters.
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