Gambian President Yahya Jammeh is refusing to step down despite the threat of military intervention by neighbouring states.
Adama Barrow, who beat him in elections last month, is due to be inaugurated as the new president on Thursday, but Mr Jammeh has ignored the deadline.
West African military forces are ready to enforce a transfer of power.
Mauritanian President Mohamed Ould Abdel Aziz failed to break the deadlock at last-minute talks with Mr Jammeh.
Mr Abdel Aziz flew in to the Gambian capital Banjul on Wednesday evening to meet Mr Jammeh before flying on to Dakar airport for further discussions with Mr Barrow and Senegal’s President Macky Sall.
“I am now less pessimistic [that Mr Jammeh] will work on a peaceful solution that is in the best interest for everyone,” Mr Abdel Aziz said.