MOGADISHU (Reuters) - Gunmen shot dead three Somali elders on Friday who were helping local aid workers distribute food in a refugee camp outside Mogadishu, witnesses said.

The shooting, by unknown men, appeared to be the latest deliberate attack on humanitarian efforts in the Horn of Africa nation where an Islamist-led insurgency is raging and more than one million people live as internal refugees.

Witness Abdikafi Hassan said one of the elders died on the spot, while the other two passed away in hospital.

"We suspect the elders were killed by the same gunmen who have been targeting aid workers," he added of the three, who were local leaders among the refugee community.

A wave of assassinations of senior local humanitarian workers has shocked aid agencies and forced many to consider suspending operations. Four foreign aid workers -- two Italians, a Kenyan and a Briton -- are also being held hostage.

Suspicion has often fallen on Islamist insurgents, whom the government says have links to radicals including al Qaeda.

Insurgent leaders accuse government hardliners of masterminding the attacks in a bid to scare the international community and hasten the arrival of a peacekeeping force.

The African Union (AU) has 2,200 peacekeepers in Somalia, but they have done little to stem the violence and the continental body wants to hand over to the United Nations.

In typical violence rocking Mogadishu virtually daily, a stray mortar landed on a shack on Thursday, killing a mother and her three sons, during an Islamist attack on Ethiopian troops, who are supporting the Somali government, witnesses said.

"The mortar shell melted their house made of iron sheets. The father and three other children sustained light injuries," witness Ahmed Mohamed said.

At least four Islamists also died, witnesses said.

"DIRE CROSSROADS"

Sheikh Abdirahim Isse Adow, a spokesman for the Islamists, said only two of their fighters had died whereas "many" Ethiopians had been killed. "We attacked our enemies from various angles, killing many of them," he said.

The Ethiopian government, which has thousands of troops in Somalia, seldom comments on its casualties there.

Somalia, with a population of 9 million, has had no effective central rule and has been in a state of near-perpetual conflict since the 1991 toppling of dictator Mohamed Siad Barre.

A spokesman for the Islamists' militant wing, al Shabaab, confirmed that a Kenyan militant in its ranks had died during fighting this week in the southern town of Berdale. "We lost Musa, a Kenyan national and a great Muslim fighter," Sheikh Mukhtar Robow said, without giving more details.

The United Nations warned on Friday that attacks on aid workers and threats from pirates to ships delivering food to Somalia were jeopardizing the lives of millions in need.

"Somalia is at a dire crossroads," Peter Goossens, Somalia director for the U.N. World Food Programme, said in a statement.

"If sufficient food and other humanitarian assistance cannot be scaled up in the coming months, parts of the country could well be in the grips of disaster similar to the 1992-1993 famine, when hundreds of thousands of people perished."

WFP said insecurity was exacerbating an already dreadful situation of failed harvests and high prices. By the end of the year, some 3.5 million Somalis would need food aid, it added.

"Families are increasingly hungry because they cannot afford to buy food, even if available in markets ... Villagers are resorting to eating wild tubers usually eaten by wild animals."

(Writing by Guled Mohamed and Andrew Cawthorne in Nairobi; editing by Philippa Fletcher)

(For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/)

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