In an exchange of gunfire, national government troops stationed on Anjouan, one of the three semi-autonomous islands that make up Comoros, clashed with local police on Wednesday, according to local media. Elections for each island are scheduled in June, but the archipelago's delicate power-sharing agreement hangs in the balance.

Heavily outnumbered national army forces had taken control of Anjouan government offices, including the ministries of justice and finance, in the island capital, Mutsamudu, before being driven off by forces loyal to the island's outgoing president, Said Bacar. No casualties were reported.

"About 50 soldiers of the national army kept the buildings from seven in the morning until three in the afternoon. Then the Anjouan [police] attacked, and by seven in the evening Bacar had taken control. There was gunfire, and they fired rockets," Aboubakar Abdoumsa, legal advisor to the president of Grande Comoros, the main island, told IRIN.

This latest standoff between national and local authorities follows the start of electoral campaigning on Monday for the presidency of each individual island. There are now fears that voting, scheduled for 10 June, will need to be postponed.

The islands of Anjouan and Moheli declared independence from Grand Comore in 1997, but the secessionist crisis was resolved with an agreement brokered in 2001 by the African Union's predecessor, the Organisation of African Unity. The agreement gave the each of the islands their own semi-autonomous government and president, with a rotating presidency for the Union.

After 19 successful and attempted coups during the past three decades, Union presidency elections in April 2006 were aimed at ending the strife and inter-island mistrust that have characterised the political landscape of the Comoros since they won independence from France in 1975.

Ahmed Abdallah Sambi, the current Union president, who comes from Anjouan and is known affectionately as 'The Ayatollah', won the 2006 election in a landslide victory when the Union presidency moved from Grand Comore to Anjouan. The elections were seen as Comoros' first real test of democracy.

Last week, the Comoros constitutional court approved 31 candidates to contest the individual island elections: 18 for Grande Comore, eight for Anjouan and five for Moheli. Bacar, who took power in 2001 as president of Anjouan island, was asked to step down by the court on grounds that he had fully served his five-year term, and nominated an interim president to head the island's government until the upcoming elections had been held.

With harbours and airports on the island closed, "no electoral committee or organisation can reach Anjouan", Abdoumsa said. "The [presidential] candidates from Grand Comore had a meeting today [Thursday] and will meet with [Union president] Sambi to ask whether elections will continue," said a political analyst, who wished to remain unnamed.

Local island authorities claim that Sambi has been slow to implement the power-sharing agreements between the islands. "He [Sambi] has refused to transfer power on issues like security and financial management to local [individual island] authorities. There have been no discussions between the island presidents and the Union president since December [2006] - this could move the Comoros back 10 years in history," the analyst added.

In February, the European Union (EU) warned in a statement, "The EU is concerned by the recent political tensions between the Union of the Comoros and its member autonomous islands, arising from disagreement over the application of the institutional laws on the distribution of powers between Union and islands."