* Frustrated lawmakers say government failing on promises
* Vote of no confidence would be setback to fragile recovery
By Abdi Sheikh
MOGADISHU, May 17 (Reuters) - Somalia's prime minister is expected to face a vote of confidence next week, lawmakers said on Friday, and backers of the challenge said they were frustrated with the pace of political reform.
Prime Minister Abdi Farah Shirdon Saaid heads a fledgling government Western capitals say is the best the strifetorn country has had for decades, determined to improve security, impose the rule of law and end corruption.
A vote against the prime minister could threaten the delicate recovery of a nation Western powers have long seen as a launchpad for militant Islam across east Africa and beyond, analysts said. One said Saaid was likely to survive.
"(The government) vowed to tackle many things in the first six months but they have achieved nothing," said legislator Dahir Amiin. "The ministers just sit on their seats, they do not know what is going on."
Other lawmakers confirmed the motion had been filed and said a debate in the 275-seat chamber was expected on May 22.
The prime minister's office was not immediately available for comment. Saaid was a relative newcomer to politics when he was appointed in October last year and widely viewed as untainted by the clan rivalries that plague Somalia.
Amiin said about 100 parliamentarians backed the motion against the prime minister. He singled out what he said was the government's failure to pay the armed forces battling al Qaeda-linked militants as a key disappointment.
Tensions have also escalated between Mogadishu and the outlying regions over how much central power should be devolved to the provinces, in what analysts said boiled down to a struggle to control resources.
A vote of no confidence would be a blow to Somalia as it strives to shake off the tag of "failed state" after more than 20 years of civil war and anarchy.
"It would disrupt whatever progress has been made over the last eight months and hurt international confidence in Somalia," said Abdi Aynte, director of the Mogadishu-based Heritage Institute for Policy Studies think-tank.
That sentiment is echoed by Saaid's backers in the chamber.
"Our government is now recognized internationally. If the parliament starts dismantling it, the world will see us as chaotic," said lawmaker Khalif Mohamed.
A security analyst predicted the prime minister would survive the vote.
"The vote will fail," the analyst said. "This is not a massive rebellion in parliament, it is the first shot by MPs who are uneasy with the government's policy and approach." (Additional reporting by Drazen Jorgic and Richard Lough in Nairobi; Writing by Richard Lough; Editing by Andrew Roche)
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