L'AQUILA: Barack Obama and fellow rich nation leaders unveiled a 20 billion dollar fund to help feed the developing world on Friday as they were urged to help the poor survive the downturn.

On the last day of the G8 summit in Italy, the US president and his peers tried to answer criticism they had turned their backs on those most vulnerable to the global economic crisis and held talks with African leaders.

As Obama prepared to embark on his first visit to sub-Saharan Africa, delegates said he played a key role in persuading around 30 countries to bankroll a fund aimed at helping smallholder farmers increase crop yields.

Initially expected to total 15 billion dollars, Obama said that figure had now reached 20 billion.

The United States will reportedly stump up around 3.5 billion dollars of the cash and Japan and the European Union between three and four billion each.

"We have committed to investing 20 billion in food security, agricultural development programmes to help fight world hunger. This is in addition to the aid we provide," said Obama.

"Going into the meeting we had agreed to 15 billion. We exceeded that mark and obtained an additional five billion of hard commitments."

The fund signifies a shift in focus by richer nations away from food aid towards practical help for local agriculture.

"We believe that the purpose of aid must be to create the conditions where it's no longer needed to help people become self-sufficient, provide for their families, and lift their standards of living," said Obama.

Kanayo Nwanze, head of UN agricultural agency IFAD, was among those who welcomed the launch, saying the plan represented a "shift from food aid -- which is like providing medication after the child is ill -- to providing assistance to help the countries... produce food by themselves."

British Prime Minister Gordon Brown said there was an urgent need for action to combat the hunger "that is now gripping over a billion people" worldwide.

"It's unacceptable that today people should go hungry in a climate as fertile as ours," he said.

Aid agency Oxfam had initially bemoaned the amount of time devoted to Africa at the summit but later changed its tune, saying G8 and other leaders had "upped their game today."

"Much of this funding is recycled, but the new money makes a downpayment on eliminating hunger," said spokesman Gawain Kripke.

Irish pop star Bono, a longtime Africa aid campaigner, hailed Obama's contribution.

"Of all the enemies of civilisation, hunger is the dumbest, the most mocking of all we hold true," said the U2 frontman.

"We are delighted President Obama has returned to this, the most fundamental of rights, with a stimulus package for the agricultural sector that is smart and innovative. But he can't do it alone."

At the talks between the African leaders and the G8, veteran Egyptian President Hosni Mubarak called for a freeze of repayments on loans to African countries to help them weather the downturn.

Mubarak asked the rich countries to "arrange a temporary freeze on African debt" and to extend credit to the continent on preferential rates.

Obama, whose father was Kenyan, and his wife Michelle, a descendant of African slaves, were to leave for Ghana later Friday on the first visit to sub-Saharan Africa by a black US president.

Before flying out from Rome however, they travelled to the Vatican for their first audience with Pope Benedict XVI.

Meanwhile, hundreds of Italian carabinieri police deployed along the route of a march by anti-globalisation protesters towards the summit venue.

Around 5,000 anti-globalisation protesters and local residents set off from Paganica, where one of dozens of tented camps have been set up to house victims of the devastating April 6 earthquake, but there were no reports of violence.

The three-day summit has been dominated by the global downturn and disagreements over how to meet greenhouse gas emissions targets.

On Thursday, Obama said the world's biggest economies had reached a "historic consensus" on cutting pollution, saying rich nations had a duty to set an example, as the leaders also agreed to shun protectionism.

The decision to stage the summit was seen as a major gamble by Berlusconi, especially as aftershocks had been felt only days before it began.

But afterwards, the premier expressed deep satisfaction at how events had gone and revealed that he planned to spend his summer holidays in the region to oversee reconstruction efforts.