(Adds protests near Mogadishu)
NAIROBI, July 15 (Reuters) - The killing and kidnapping of aid workers in Somalia threatens to wreck all attempts to resolve a humanitarian disaster that could soon rival its famine in the early 1990s, the United Nations said on Tuesday.
Most aid agencies are discussing suspending their operations in areas hit by mounting insecurity and a wave of assassinations that has targeted senior local humanitarian workers.
Relief is still getting through, but the U.N. World Food Programme (WFP) said the surge in violence was threatening the entire humanitarian response to the emergency.
"If we or our partners cannot operate on the ground because they are being shot or kidnapped then assistance will not be distributed," WFP spokesman Peter Smerdon told Reuters.
"If sufficient assistance cannot be delivered ... in the coming months, parts of southern and central Somalia could well be gripped by a disaster similar to the 1992-1993 famine."
Hundreds of thousands died then.
Since the start of last year, more than 8,000 civilians have been killed in fighting after Ethiopian troops helped the interim government drive an Islamist movement out of Mogadishu.
One million Somalis have been forced from their homes by the latest bloodshed -- their situation is worsened by banditry, drought, high food and fuel prices and inflation.
The latest aid worker victim was an employee of a trucking company working for WFP who was killed on Sunday by militiamen manning a checkpoint near the southern town of Buale.
That was the fifth such murder this year of WFP-contracted transport workers.
Four foreign aid workers -- two Italians, a Kenyan and a Briton -- are being held hostage in the Horn of Africa nation.
But it is the recent assassinations of senior local aid officials, combined with the appearance of threatening leaflets, that have made people even more afraid.
On Friday, men armed with pistols shot dead the deputy head of a German charity and another local man working for a WFP partner group. A week earlier, gunmen had killed the local head of the U.N. Development Programme (UNDP) in a similar attack.
Hundreds of displaced Somali women and children protested outside their squalid camps near Mogadishu against the attacks, fearing they will worsen their already dire plight.
"Those killing aid workers are indirectly exterminating us," protester Asha Abdullahi told Reuters. "We have not seen any aid workers since yesterday. Our water reservoirs are almost empty. We fear dying of thirst and hunger."
Suspicion for the killings and kidnappings usually falls on the al-Shabaab, Islamist rebels waging an Iraq-style insurgency against the government and its Ethiopian allies.
But there is confusion over the identities of those behind the recent murders. Leaflets circulated in the Shibis area of the capital last week threatened local aid workers with death if they did not publicly resign from the jobs.
Although supposedly from an insurgent group, they used no Islamist phrases.
The Islamists have accused government hardliners of ordering the latest killings to spur the international community into sending a robust peacekeeping force to help it stay in power.
Somali officials deny that.
Last month, an al Qaeda leader issued a video on the Internet urging Somalia's insurgents to fight on.
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