Violence against aid workers in Somalia has increased in recent weeks
Gunmen in Somalia have shot dead three elders distributing aid in a refugee camp on the outskirts of Mogadishu.
The killings are being linked to a wave of apparently targeted attacks on humanitarian workers.
Meanwhile, the World Food Programme has warned that it may have to use private security companies to protect its vessels from pirate attacks in Somalia.
The agency has been sending food ships without protective escorts after a Dutch naval mission ended last month.
The WFP country director for Somalia, Peter Goossens, told the BBC the threat of piracy was putting at risk vital food aid for millions of people in Somalia.
"The problem is twofold - the ships themselves can get hijacked and we lose the food... my biggest problem is that I can't find enough vessels that are willing to do this work for me unless they get an escort," he said.
Mr Goossens warned that the country was at a dire crossroads, with the risk of a famine similar to the early 1990s, when hundreds of thousands died.
He added that the UN had spoken to various naval powers who might provide military escorts to aid WFP ships, including Britain, Sweden and India.
He said he was grateful for their expressions of interest, but now wanted action.
Pirates operate off the coast of Somalia using high speed vessels and automatic weapons.
BBC World Affairs correspondent Mark Doyle says that shipping companies regularly pay ransoms of hundreds of thousands of dollars to get their vessels released.
The killings of three local leaders among the refugee community are the latest in a string of apparently targeted attacks on aid workers, which has caused a number of humanitarian agencies to consider pulling out of Somalia.
"About five masked men armed with pistols came to our camp, they ordered us to get into our make shift houses and then after a few minutes we heard shots, when we came out three of our men... were lying there," a witness, Aden Norow, told the BBC.
"We do not know why our colleagues were targeted but we suspect it is because they were active in the recent protests against the killings of the aid workers - someone wants to silence us - we do not know who," Abdow Dahir Mudey said.
Another elder was killed in a separate incident some 60km (37 miles) from the city.
It is not clear who exactly is behind Friday's killings, but a BBC correspondent says many factions in Somalia's chaotic war stand to benefit from the violence.
Meanwhile, at least 10 people were killed and 15 others wounded after fighting broke out on Thursday in southern Somalia, 100km west of Kismayo, in the Lower-Jubba region.
Somalia has experienced almost constant civil conflict since the collapse of Mohamed Siad Barre's regime in January 1991.
Successive droughts have left an estimated two and a half million in need of food aid. That figure could rise if the droughts and insecurity continue.