Gambia’s ministers of finance, foreign affairs, trade and the environment have resigned from President Yahya Jammeh’s government, state television said, as regional forces prepare to oust the veteran leader unless he steps down by Thursday.

Jammeh, in power since a 1994 coup, has become increasingly isolated at home and abroad after he refused to accept his Dec. 1 defeat to opposition leader Adama Barrow.

The surprise loss was seen as a boost to democracy in the former British colony, which has had only two presidents since it gained independence in 1965.

But Jammeh’s defiance has sent the tiny West African country into crisis, causing government defections and opening up the prospect of military intervention by other countries in the region.

A senior Nigerian military source said Nigeria and other West African nations were prepared to intervene militarily to remove him if he remains in office after Wednesday, when his presidential mandate runs out.

“The chiefs of defence 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 Nigerian source, who declined to be identified.

“Some West African countries will be contributing troops, including Nigeria, for the operation,” said the source, adding that the United Nations and African Union had offered support to regional body ECOWAS for the plan.

Gambian state television said late on Monday that Finance Minister Abdou Kolley was being replaced. Ministry sources said other government leaders including Foreign Minister Neneh Macdouall-Gaye had 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, according to sources at the city council.

(Addtional reporting by Felix Onuah in Abuja; Editing by Edward McAllister and Andrew Roche)