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By Abdi Mohamed and Ibrahim Mohamed

MOGADISHU, July 1 (Reuters) - Somali gunmen have kidnapped five local employees of an Italian charity and the United Nations in the latest attack on humanitarian staff in the country, the head of the Italian group said on Tuesday.

Elio Sommavilla, founder of the Water For Life (WFL) charity, told Reuters four of those kidnapped worked for his charity, identifying the fifth as an agronomist with the U.N. Food and Agriculture Organisation (FAO).

The FAO in Rome could not confirm the kidnapping.

Witnesses had earlier said two Somalis, a man and a woman, had been kidnapped when a dozen men with rifles stopped them on their way to Mogadishu on Monday and turned their two cars into the bush near Afgooye, west of the capital.

"I could see the two cars marked 'WFL' being hijacked," bus driver Hassan Osman said.

Suspicion for kidnappings generally falls on clan militia and Islamist insurgents who are fighting the Somali government and their Ethiopian military allies.

Gunmen are still holding hostage four foreign aid workers -- two Italians, a Kenyan and a Briton -- and another three Somalis abducted in April and May.

Two U.N. workers from Sweden and Denmark were briefly taken on Saturday in south Somalia, until local elders and colleagues negotiated their release with Islamists.

Mired in anarchy and awash with weapons since the 1991 overthrow of dictator Mohamed Siad Barre, south Somalia is off-limits for all but a small band of foreign aid workers, and local staff face extreme risks by association.

Sommavilla said two of the kidnapped Somalis had been due to fly to Italy on Tuesday to receive an award. The WFL charity trains Somali geologists.

Kidnapping is lucrative business in Somalia, with hostages generally treated well in anticipation of a large ransom.

On Tuesday, Islamist insurgents clashed with a convoy of Ethiopian soldiers passing through the central Hiraan region. At least one senior rebel commander was killed and some Ethiopian vehicles were burned, residents and an official said.

The Somali government, which is backed by the Ethiopian military, had no immediate comment. An Islamist spokesman confirmed three deaths including that of Moalim Farhan, a commander in the north-central Galgadud region.

It was impossible to get an accurate independent account of the casualties on both sides.

The kidnappings and attacks are hampering the operations of aid agencies at a time when U.N. officials say Somalia ranks as one of the world's worst humanitarian crises along with Sudan's Darfur region, Congo, Iraq and Afghanistan.

Over 1 million of Somalia's 9 million people live as internal refugees, and their plight has been worsened by record food prices, hyper-inflation and drought.

The insurgency has killed 2,136 civilians so far this year, bringing the death-toll since it began in early 2007 to 8,636, according to a local human rights group. (Additional reporting by Abdi Sheikh in Mogadishu and Silvia Aloisi in Rome; Writing by Andrew Cawthorne; Editing by Ibon Villelabeitia) (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com)

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