The talks will be led by Guinean president Alpha Conde in the Gambian capital Banjul on Friday morning.
The talks will be led by Guinean president Alpha Conde in the Gambian capital Banjul on Friday morning, according to Marcel Alain de Souza, head of the Economic Community of West African States.
"We have suspended operations and given him an ultimatum," said de Souza, who attended the swearing-in of The Gambia's new president Adama Barrow on Thursday.
"If by midday, he doesn't agree to leave The Gambia under President Conde we really will intervene militarily," he added.
De Souza said there had been "a few warning shots so far" and it was "out of the question that he remains where he is".
"What we are asking is for him to leave," he added.
Conde will first travel to Mauritania where he will meet the country's president Mohamed Ould Abdel Aziz -- who led the previous round of negotiations with Jammeh on Wednesday -- and then to Banjul.
Both Conde and Aziz are "opposed to military intervention, preferring a diplomatic solution to the crisis", according to an official Mauritanian source.
Gambian state broadcaster GRTS Thursday announced the arrival of a high-level delegation from Liberia, Mauritania, Guinea and the United Nations for talks aimed at "finding a peaceful solution to the current political deadlock", according to an official statement.
"No one should panic, the situation in the country is under control", the statement said.