President Jammeh won the last elections with 53% of the vote

Coalition spokesman Ousainou Darboe said the opposition realised it must unite to have a chance to win.

The opposition have yet to announce their candidate, but Mr Darboe said many people have become disenchanted with President Yahya Jammeh.

He came to power in a coup in 1994 and won a second term in office in October 2001 with 53% of votes cast.

'System change'

Mr Darboe - the leader of the United Democratic Party - was Mr Jammeh's main rival in the last elections, taking 33% of the vote.

Gambians are disenchanted, Gambians need a change Ousainou Darboe United Democratic Party leader

The opposition coalition failed in 2001 because not all parties were on board, however the National Alliance for Democracy and Development was united, he said.

"This time around we have all realised that it is in the best interests of the Gambia to have all the opposition parties coalesce and fight the next general elections in 2006," Mr Darboe told the BBC's Network Africa programme.

The coalition's objective was not simply to remove the president from office, but to have concrete policies - as their manifesto due out in a month's time would reveal, he said.

"We are not interested in regime change, we are interested in a complete system change."