The African Union has said it will no longer recognise The Gambia’s President Yahya Jammeh as the country’s leader from next Thursday, when his term ends.
AU warns of “serious consequences” if Mr Jammeh’s refusal to give up power causes a crisis.
Adama Barrow, who won the recent presidential vote, said he believe he would be sworn in next week.
Nigeria’s president Buhari has flown to Banjul to try to broker a deal but the latest talks appear to have failed.
Nigerian MPs have voted to offer Mr Jammeh asylum to help negotiations.
Mr Jammeh had initially conceded defeat after the 1 December election but later changed his mind. He wants the results of the election annulled after the electoral commission admitted some errors, although it insists this did not affect the final outcome.
The 51-year-old leader seized power in the country in 1994 and has been accused of several human rights abuses.
The Supreme Court is unable to hear the challenge until May because of a shortage of judges, and Mr Jammeh says he will not step down until then.
Meeting in the Ethiopian capital Addis Ababa, the AU peace and security council called on Gambia’s security forces to exercise restraint.
In a statement, it warned of “serious consequences in the event that his [Mr Jammeh’s] action causes any crisis that could lead to political disorder, humanitarian and human rights disaster, including loss of innocent lives and destruction of properties”.
There are growing fears that the uncertainty could cause a refugee exodus.
Thousands of Gambians, mostly women and children, have already crossed the border into neighbouring Senegal and further away to Guinea-Bissau, where they do not require a visa, officials say.