Nigeria and some other African countries are preparing a joint force to intervene militarily in the Gambia if President Yahya Jammeh does not hand over power to opposition leader, Adama Barrow.
A Nigerian military source said on Tuesday that West African countries could launch the military intervention if Jammeh did not step down when his five-year mandate ends on January 18.
"The chiefs of defense staff of West African countries met yesterday (Monday) to discuss strategies on the best way to get Yahya Jammeh out if he refuses to hand over power," said the unnamed Nigerian source, adding, "Some West African countries will be contributing troops, including Nigeria, for the operation."
"A decision has been taken that he will not remain president of Gambia at the expiration of his tenure."
The source said the United Nations and African Union had offered support to the Economic Community of West African States (ECOWAS) for the intervention.
Jammeh had initially accepted the results of the December 1, 2016 election, in which Barrow was declared the winner, but later reversed his position and lodged a complaint with the Supreme Court over election irregularities.
In the meantime, the possibility of military intervention in the Gambia gained strength after the UN and the African Union both called on the Gambian incumbent leader to accept the result of the vote and leave after 22 years in power.
Jammeh's defiance has sent the West African country into crisis, causing defections.
The Gambia's ministers of finance, foreign affairs, trade and the environment have resigned from the Jammeh administration.
State television said late on Monday that Finance Minister Abdou Kolley was being replaced. Other government leaders, including Foreign Minister Neneh Macdouall-Gaye, have left the government and the country. Their departures follow the resignation of Communications Minister Sheriff Bojang last week.
The mayor of the capital, Banjul, has also resigned amid ensuing crisis in the country.