By Ahmed Ali Amir

MORONI, March 24 (Reuters) - Some 1,350 African Union (AU) troops from Tanzania and Sudan have arrived in the Indian Island archipelago Comoros ready for an assault on the rebel island of Anjouan, a senior military source said.

With the backing of the continental body, the national government of coup-prone Comoros has for weeks been threatening to land on tiny Anjouan and topple its local leader, Mohamed Bacar, who clung to power in an illegal election last year.

National President Ahmed Abdallah Mohamed Sambi has plenty of support at home and in the AU for an operation against the hilly, tropical island held by Bacar and his militia.

"The 750 Tanzanians and the 600 Sudanese have all arrived," Lieutenant Colonel Normal Mze, a military assistant, told Reuters late on Sunday. A Senegalese contingent was also due.

Despite general backing around the region, continental heavyweight South Africa has expressed reservations about an assault on Anjouan, saying dialogue would be preferable.

And the party of Comoros' former national president Colonel Azali Assoumani also questioned the wisdom of an attack.

"The use of any force.. would attract the attention of the population of both Comoros and the international community to the groundless character of a fratricidal war whose motives are not convincing," it said in a written statement.

The central government accuses Bacar of secessionist aspirations, but the former French-trained gendarme says he wants more autonomy for Anjouan rather than independence.

Analysts say the African Union may be hoping to score a relatively easy victory against Anjouan to earn some much-needed international prestige to offset the failures of its struggling peacekeeping missions in Sudan and Somalia.

After suffering some 20 coups or coup attempts since independence from France in 1975, Comoros is trying to shrug off a history of instability and inter-island bickering.

Lying off Africa's east coast, the islands -- which grow vanilla, cloves and ylang-ylang, a flower whose oils are used in aromatherapy -- were first settled by Arab seafarers 1,000 years ago, then later became a pirate haven. (Writing by Ed Harris; Editing by Andrew Cawthorne) (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/)

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