* U.N. says impossible to consult people on new constitution
* Refuses calls for extension to government mandate
* 4,000 extra AU troops expected March earliest
By Richard Lough
NAIROBI, Jan 26 (Reuters) - The United Nations acknowledged on Wednesday that Somalia would miss an August deadline to adopt a new constitution and hold the first elections in the Horn of Africa nation for decades.
Under the terms of a 2009 deal, the mandate of Somalia's Transitional Federal Government (TFG) expires on Aug. 20, by which time it should have enacted a new basic law and held a general election.
But a raging insurgency has seen the government do little more than battle for survival, while tens of thousands of civilians have been killed over the past four years.
There have been calls from some parts of the government for its term to be extended. Augustine Mahiga, the U.N.'s special representative for Somalia, said this was not an option and talks were needed on what shape the next government takes.
"The constitutional process should have been our ideal path but ... we don't want a half-baked document to define the destiny of Somalis," he told a news conference in the Kenyan capital Nairobi.
"We are all agreed this (interim administration) has to end."
With al Shabaab militants controlling huge chunks of central and southern Somalia, as well as half the capital Mogadishu, it had been impossible to consult the population on the draft document, Mahiga said.
He said U.N. Secretary-General Ban Ki-moon would convene a special meeting on the sidelines of this weekend's African Union summit in Addis Ababa to discuss Somalia.
NAIROBI SUMMIT
The United Nations would then convene a summit in Nairobi, inviting TFG leaders, officials from the semi-autonomous Puntland region and breakaway enclave of Somaliland, and the international community to thrash out a way forward.
The next administration would have to be more inclusive, Mahiga said, urging President Sheikh Sharif Ahmed, himself a former Islamist rebel, to open government's doors to moderates within the two main rebel factions.
"The political outreach and reconciliation must proceed. There are nationalists who are there (within al Shabaab) ... but this is up to government who they talk to," said Mahiga.
Political analysts say al Shabaab is split between a nationalist element fighting to topple the Western-backed government and more extreme jihadists bent on wreaking havoc across the region.
Up to a million people have been killed by fighting, famine and disease in the 20 years that Somalia has lacked an effective central government, according to the International Committee of the Red Cross (ICRC).
Mogadishu's two main referral hospitals treated more than 6,000 war-wounded in 2010, 20 percent higher than the previous year, with women and children making up a third of those caught up in gun battles, artillery fire and landmine explosions.
Mahiga said the 4,000 additional African Union peacekeepers approved by the U.N. Security Council last month would not deploy until March or April at the earliest, bringing the AMISOM force to 12,000 troops.
Critics say without elections, the next administration will just be Somalia's 16th transitional government since 1991.
"The alternative is to roll over, said Mahiga. "We want something that is different ... something that is more inclusive."
(Editing by David Clarke/Maria Golovnina)
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