Kenya's prime minister said Saturday he was under mounting pressure to close the border with Somalia as he joined other African leaders pleading for help to counter a spreading famine.

With tens of thousands already dead and a camp in Kenya now housing 500,000 famine refugees, Prime Minister Raila Odinga said the United Nations should set up camps inside Somalia.

Odinga and leaders from Somalia, Djibouti and Ethiopia pushed for greater international action at a UN summit on the crisis as the World Bank near quadrupled aid to the Horn of Africa countries to $1.9 billion from $500 million.

The United Nations estimates that 750,000 people are at risk of death from starvation and that 13 million need urgent help.

The Dabaab camp in Kenya has become the world's biggest refugee complex because of the famine crisis with thousands arriving each week.

Kenya has "a problem" with the UN High Commissioner for Refugees (UNHCR) over the location and cost of camps, Odinga said at the launch of a charter to avoid hunger before summit. "We don't share their argument," he said.

"There have been a lot of pressures on us to close the border. But as a government we cannot close the border because that would mean condemning innocent people to death."

Many refugees are fleeing areas of Somalia under the control of Shebab Islamist insurgents who have restricted access to the UN and private aid groups.

Odinga said however that there are growing problems getting water and fuel for Dabaab which was designed to house 90,000 people.

"We are calling for much stronger collaboration among the international community to deal with this, so that we can create another zone within Somalia and put up tents and camps there."

He said the international community should send supplies "so that people can be fed in Somalia so that they don't have to cross the border to come into Kenya."

But UN Humanitarian Coordinator Valerie Amos said the United Nations opposed opening camps in Somalia.

"Kenya has been very generous in terms of hosting refugees from Somalia since 1991," she said.

UN agencies were seeking to increase the number of people getting food and healthcare in Somalia, but Amos said the UN was "not in favour" of camps on the Somali side of the border.

Somalia's Prime Minister Abdiweli Mohamed Ali told the UN summit that another 500,000 people have fled to the capital Mogadishu, where government forces and African Union troops have taken control of most zones from Shebab fighters.

UN Secretary General Ban Ki-moon said the "crisis grows deeper by the day" across the Horn of Africa as he appealed for greater international financial assistance.

He said $750 million dollars would be needed to provide food and medicine this year and even more next year.

The World Bank said its extra finance would be spread over three years with $288 million in "rapid response" funds to be given between now and next June.

Bob Geldof, the rock singer who organized the Live Aid concerts to raise funds for Africa in 1985, also appeared at the "Charter To End Extreme Hunger" and said the western world was allowing a "grotesque horror" in the Horn of Africa.

"It is bewildering for me to be talking like this 25 years later," Geldof said at the ceremony where the Kenyan prime minister became the first government leader to sign the charter drawn up by a group of aid agencies.

"There seems to be a perfect storm of social challenges confronting us ... ones that we appear to be incapable of dealing with," Geldof said, blasting "a chronic lack of leadership by the governments of the world."