Four African Union countries have said they will give military backing to the Comoros government in its attempt to end a rebellion on Anjouan island.
The federal government is losing patience with the Anjouan revolt
Anjouan, one of the three islands that make up the Comoros, held its own election in June last year in defiance of a central government order.
Tanzania, Senegal, Libya and Sudan said they had agreed practical, military and security plans to back the government.
The mission will be under the AU, which has already put sanctions on Anjouan.
Mohamed Bacar was re-elected president of Anjouan - which together with the islands of Grande Comore and Moheli forms the Union of Comoros - in the controversial election last year.
Correspondents say the federal government is losing patience and has been preparing its troops for an assault on the island, home to around 300,000 people.
Ministers from the four countries met for talks at the African Union in the Ethiopian capital, Addis Ababa, on Thursday.
Tanzanian Foreign Minister Bernard Kamillius Membe said that after seven and a half hours of deliberations, the four nations had resolved to help Comoros President Ahmed Abdallah Sambi to "restore peace and security in Anjouan as soon as possible".
The AU said the countries had agreed to "despatch immediately a military and security assessment and planning team to the Comoros to finalise the planning process".
It gave no further details of the planned mission, but Comoros Foreign Minister Ahmed Jaffar told Reuters news agency that former colonial power France had volunteered to transport the AU troops.
Mr Bacar declared himself the winner of June's polls
The Comoros government's top military officer said earlier this week that an attack on Anjouan was "imminent".
Hundreds of soldiers have gathered on Moheli, the island nearest Anjouan.
A history of political violence has left the Comoros desperately poor.
At times, the country has teetered on the brink of disintegration, amid tensions between the semi-autonomous islands and the central government.