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.
Senegalese troops remain stationed at the Gambian border, despite the deadline for Mr Jammeh to stand down passing at midnight.
The threat of military action is supported by Nigeria and other states in the region.
However Gambian army chief Ousman Badjie said his troops would not fight Senegalese forces should they enter into the country, AFP news agency reports.
"We are not going to involve ourselves militarily, this is a political dispute," he said. "I am not going to involve my soldiers in a stupid fight. I love my men."
Mr Jammeh has ruled The Gambia since taking power in a coup in 1994.
Wednesday was meant to be his last day in office but parliament granted him three more months in the post.
Mr Barrow, who was said to be preparing to be sworn in as president "on Gambian soil" on Thursday, remains in neighbouring Senegal.
At least 26,000 Gambians, fearful that violence could erupt, sought refuge in Senegal this week.
Meanwhile, thousands of UK and Dutch tourists continue to be evacuated from the tiny West African state on special charter flights. Gambia is a popular beach destination among European holidaymakers, especially in winter.
Nigeria says it sent fighters and other aircraft, along with 200 personnel, to Senegal on Wednesday morning.
Nigerian navy vessels are also on standby and a warship that sailed from Lagos on Tuesday will have the task of evacuating Nigerian citizens while putting on a show of force.
Ground troops are also being provided by Ghana.