Gambian President Yahya Jammeh is refusing to step down despite efforts to persuade him to leave office ahead of a deadline set by Senegal.
Adama Barrow is due to be inaugurated as the new president on Thursday, and West African military forces are poised to move in.
Mauritanian President Mohamed Ould Abdel Aziz met Mr Jammeh for last-minute talks before flying on to meet Senegal’s President Macky Sall.
Mr Barrow won elections last month.
Senegalese troops remain stationed at the Gambian border, as the deadline for Mr Jammeh to stand down passed 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.
West African leaders hold crisis talks
Mauritanian President flew to Senegal to meet with President Macky Sall after last-ditch talks in Gambia aimed at resolving a crisis over the transfer of power.
Aziz left Gambia shortly before midnight, when Gambian leader Yahya Jammeh’s presidential mandate expired.
Senegal, with backing from leaders in the region, has threatened to invade Gambia to depose Jammeh if he does not immediately hand over power to challenger Adama Barrow, who beat him in an election in early December.
After the talks, Aziz’s plane left Dakar at about 1:45 a.m.(0145 GMT), a Reuters witness saw. Aziz had been talking with Barrow and Sall at the airport in Dakar. About 30 vehicles with tinted windows then sped away from where the talks took place.
The Gambian capital Banjul, a city of tourist hotels and sleepy streets shaded by mango trees, was silent apart from the occasional military helicopter buzzing overhead.
Facing almost total diplomatic isolation, a government that has all but collapsed from defections and the looming threat of a military intervention by his neighbours, it was unclear what might be Jammeh’s next move.