The Gambia's opposition parties announced Friday they would unite around a single candidate for December's presidential election, in an unusual show of unity as President Yahya Jammeh seeks a fifth term in power.



At a meeting in Banjul, the groups agreed to pick a single contender at a convention on October 30, just weeks ahead of the election slated for December 1.



The signatories of the memorandum said they were "putting our differences aside, in pursuance of the supreme national interest", with the aim of ousting Jammeh from power.



They included the United Democratic Party (UDP) -- the country's principal opposition movement -- along with several smaller groupings and the Gambia's first ever female presidential candidate, development expert and women's rights campaigner Isatou Touray.



Jammeh came to power in a 1994 coup, and has ruled The Gambia with an iron fist ever since.



Before the nation's last presidential vote in 2011, the 15-nation Economic Community of West African States (ECOWAS) said Jammeh's control of the media and intimidation of voters meant the election could not be free and fair.



The strongman took 73 percent of the vote.



The Gambia's newly appointed Independent Electoral Commission assured political parties last month the vote would not be rigged, despite fears that an opposition crackdown is already underway.



Commissioner Alieu Momar Njie told reporters in Banjul: "The stakes may be high, and temptation may be great to achieve victory through illegal or morally questionable means in some countries.



"I stand here today to pronounce to you that, as far as our concerted efforts are in play, this will never be the case in our dear country."

UDP party leader Ousainou Darboe -- the runner-up in 2011 -- is among several opposition figures serving three-year sentences for organising a peaceful rally over two party members' deaths in custody.



The UN, France, the US and human rights watchdogs have all voiced concern over the deaths and called for an independent probe.



Campaigning for the election begins on November 16.



Since independence from Britain in 1965, the Gambia has had just one other leader: Dawda Jawara, who served until the current president toppled him in the 1994 coup.