The African Union will cease to recognise Gambia's Yahya Jammeh as the nation's legitimate president as of January 19.
It is the date he is due to hand power to Adama Barrow, the winner of the December 1 election.
The AU's Peace and Security Council made this declaration after a meeting in Addis Ababa, the Ethiopian capital.
The council also warned of "serious consequences in the event that his action causes any crisis that could lead to political disorder, humanitarian and human rights disaster, including loss of innocent lives and destruction of properties".
The AU declaration came on a day that President Muhammadu Buhari led a delegation of West African leaders to Banjul, Gambian capital, with the aim of persuading the soldier turned politician, to hand over power to Barrow.
Mr. Jammeh's political party, in the latest gambit, has gone to court to halt the inauguration of Mr. Barrow, on the basis that Mr. Jammeh's challenge of the electoral result, has not been decided by the country's Supreme Court.
The case was adjourned for months, because the court could not form a quorum.
Meanwhile, opposition politicians are trying to offer some carrots to encourage Mr. Jammeh to leave power peacefully.