* Addis Ababa sent in tanks and troops in November
* AU said Ethiopia would pull out by end of April
* Kenya, Uganda, Burundi peacekeepers also fighting rebels
By Aaron Maasho
ADDIS ABABA, June 22 (Reuters) - Ethiopia plans to keep its troops in Somalia until the Horn of Africa country ratifies a constitution and its military is able to fend off militant threats on its own, an official said on Friday, signalling a change in policy.
Addis Ababa rolled hundreds of troops across its border in November to open up a third front against the al Qaeda-allied al Shabaab group but was keen to point out their incursion is not a repeat of their ill-fated 2006-2009 war in Somalia.
Ethiopian officials have said their troops would only be deployed for a brief period to fight Islamist militants who are also fighting thousands of Ugandan and Burundian troops under the African Union Mission in Somalia (AMISOM), as well as Kenyan forces to the south.
"It (Ethiopia) will remain (in Somalia) until the Transitional Government (of Somalia) has adequately organised itself to fend off any attack from hostile forces," government spokesman Shimeles Kemal told reporters.
"There is no current plan to evacuate from Somalia until such time that a proper Somali constitution is ratified by all parties to the conflict, and until the constituent assembly will ratify the constitution," Shimeles sa i d.
Last June Somalia's feuding leaders agreed to extend the mandate of a transitional government for a year rather than hold elections, a move sought by Uganda which has peacekeepers stationed in the anarchic state.
The mandate for Somalia's latest administration was meant to expire in August 2011 but President Sheikh Sharif Ahmed, a former Islamist rebel leader, and speaker Sharif Hassan Sheikh Aden, who covets the top job, had been at loggerheads over what should happen then, and agreed to defer elections.
Weakened by internal divisions and financial constraints, the rebels have surrendered territory in Mogadishu and across central and southern Somalia in the past few months.
Ethiopian forces captured the rebel stronghold of Baidoa in southern Somalia in February having seized Baladwayne from the militants on New Year's Eve.
In May, AU and Somali government troops secured an aid corridor between Mogadishu and a former rebel stronghold close to the capital, wresting control of a vital strip of land believed to hold around 400,000 people displaced by conflict.
By the end of the month, Somali and Kenyan forces had captured the rebel stronghold and strategic town of Afmadow, though the militants claimed they retreated.
Seizing Afmadow was considered a crucial step in the Kenyan drive towards the southern port city of Kismayu, the hub of al Shabaab operations, about 120 km (75 miles) away.
In areas they have vacated, the militants have resorted to guerrilla-style hit-and-run attacks, launching grenade attacks and using suicide bombers.
The rebel group has waged a bloody five-year campaign to topple Somalia's Western-backed government and impose its harsh interpretation of Islamic law.
It continues to hold swathes of central and southern Somalia but is being squeezed out of some areas by Kenyan and Ethiopian troops.
Somalia has been mired in chaos since warlords toppled dictator Mohamed Siad Barre in 1991. (Editing by George Obulutsa and Louise Ireland)