African leaders held a rare fund-raiser in Ethiopia Thursday in a bid to plug a $1.1 billion shortfall in aid for millions facing starvation in the Horn of Africa's worst drought in decades.

Only four heads of state -- African Union chairman Teodoro Obiang Nguema, Ethiopian Prime Minister Meles Zenawi, Djiboutian President Ismael Omar Guelleh and Somali leader Sharif Sheikh Ahmed -- were present at the start of the meeting.

The fund-raising conference is the first of its kind by the pan-African body, which has so far pledged only a tiny fraction of the sums needed to deliver relief to the region.

"We are still not reaching all the people who need help, and the crisis still has not peaked. The cost in human suffering will rise even higher. We must do all that we can to stop the acceleration," UN deputy secretary general Asha Rose Migiro said.

"The future of an entire generation hangs in the balance," she told the conference.

"We don't want words, we want action," said Noureddine Mezni, the AU commission spokesman, calling for contributions to plug the $1.1 billion funding shortfall.

A total of $2.4 billion (1.6 billion euros) is required to assist the 12.4 million drought victims. The AU has pledged $500,000.

The AU's envoy to Somalia, the former Ghanaian president Jerry Rawlings appealed to both African governments and private sector.

"It was decided ... to seek support not only from African governments but seek significant contributions from corporate Africa," he said.

The Horn of Africa is suffering its worst drought in decades which, combined with conflict and resource mismanagement in Somalia, has led to what the UN describes as the world's worst unfolding humanitarian disaster.

The world body for the first time this century has declared a state of famine in five Somali regions and said it could spread to engulf the country's entire south.

The drought has also left millions in parts of Ethiopia, Djibouti, Kenya and Uganda facing starvation.

A pan-African fundraising campaign, Africans Act 4 Africa, criticised African governments and the AU for not responding quickly enough to a crisis that blew up two months ago.

So far, African governments have pledged $21 million, but only from a few countries, the fundraising group said in a statement, adding that Africa should offer a minimum of $50 million.

"If we truly believe in 'African solutions for African problems' we need to demonstrate this very clearly, not just in words but in actions," the group said.

"We need to ensure this is not just another talk shop where AU leaders spend a lot of money on travel, protocol and their entourages."

Somalia has been the worst affected country in the region, with nearly half of its estimated 10 million people in need of humanitarian aid and hundreds of thousands struggling for survival after fleeing to Ethiopian and Kenyan camps.

UN Humanitarian Coordinator for Somalia Mark Bowden warned Wednesday that Somalia's Middle and Lower Juba regions could be hit by famine, adding to the five regions already declared to be in famine.

European Union foreign affairs chief Catherine Ashton also Wednesday urged world governments to meet a "moral obligation" and increase emergency aid to the drought-hit Horn of Africa.

"The situation is grave, and it is a moral obligation of the international community to offer its help," she said.

Ashton said the EU's immediate humanitarian commitment for this year had risen from 97 million euros to 158 million, while national aid pledges from its member states totalled a further 440 million.