Long-ruling Gambian leader Yahya Jammeh, who lost elections last month, has until midday Friday to hand over power and agree to leave the country or face military action, regional bloc ECOWAS has said.
West African troops entered The Gambia on Thursday to bolster its new President Adama Barrow but the military operation was suspended a few hours later, in favour of a final diplomatic effort to convince Jammeh -- who has refused to quit -- to exit the country.
"We have suspended operations and given him an ultimatum," said Marcel Alain de Souza, head of the 15-nation Economic Community of West African States.
"If by midday, he doesn't agree to leave The Gambia...we really will intervene militarily," he added.
Final talks will be led by Guinean president Alpha Conde in the Gambian capital Banjul on Friday morning, according to de Souza.
Conde will first travel to Mauritania where he will meet the country's president Mohamed Ould Abdel Aziz, who led the previous round of negotiations on Wednesday with Jammeh.
De Souza said a total of 7,000 troops would be mobilised by Senegal and four other nations, a day after they first crossed into the tiny tourist-friendly country, whose army chief joined ordinary citizens celebrating in the streets seven weeks after contested polls.
The United States earlier praised the West African intervention.
"We understand that the purpose is to help stabilise a tense situation and to try to observe the will of the people in the Gambia," State Department spokesman John Kirby said.
Barrow was sworn in at The Gambia's embassy in Dakar in neighbouring Senegal Thursday after Jammeh refused to step down despite international pressure following his December election loss.
Dressed all in white, 51-year-old Barrow waved to a crowd of thousands of jubilant Gambians at an inauguration ending Jammeh's 22-year rule.
"This is a victory of the Gambian nation. Our flag will now fly high among those of the most democratic nations of the world," he said, demanding loyalty from his armed forces.
Shortly after the ceremony, the UN Security Council unanimously backed efforts by the regional bloc ECOWAS to force Jammeh to hand over power, (without formally authorising military action.)
As Barrow was sworn in, celebrations erupted in Banjul, where tensions have run high over the crisis, especially since a declaration of emergency by Jammeh on Tuesday.
Among the revellers was Gambian army chief Ousman Badjie, who had said he would not order his men to fight the African troops then poised to intervene.
"Freedom has come at last. Tyranny is buried and democracy restored," said Barrow supporter Lamin Sanyang, who had joined the crowds.
Further dispelling fears of a fight-back by factions loyal to Jammeh, a minimal troop presence was visible near Banjul and soldiers did not stop the jubilant scenes.
But on the ground armed forces including "all means, land air and sea" forces crossed into The Gambia, a Senegalese army officer told AFP, adding that Nigeria, Ghana, Togo and Mali were also involved.
A Senegalese army spokesman confirmed his country's troops had crossed the border, after Nigerian jets earlier overflew The Gambia to help force out Jammeh, whose mandate expired at midnight Wednesday.
Senegalese soldiers had entered "from everywhere", said Colonel Abdoul Ndiaye.
Barrow, an opposition coalition candidate, defeated Jammeh, who had ruled the former British colony since seizing power in a 1994 coup, in a surprise election win on December 1.
He initially conceded victory but in a U-turn then refused to step down.
On Thursday night, calls of congratulations flooded in for the new president, including from the UN Secretary-General and Britain.
Barrow, a real-estate agent turned politician, had flown into Senegal on January 15 to seek shelter after weeks of rising tension over Jammeh's stance.
Jammeh had attempted to block Barrow's inauguration with a court ruling and this week declared a state of emergency.
Jammeh's former lawyer Edward Gomez, who was arguing cases on the president's behalf as late as Monday, pleaded with him to step down Thursday after himself fleeing to Senegal.
"My humble prayer to President Jammeh is to concede to defeat," he told Senegal's 2S channel. "Please, let peace continue to reign in The Gambia."
Tour operators have continued to evacuate hundreds more tourists from the tiny country's popular beach resorts.
Arriving back from The Gambia at Manchester airport in England, several passengers could be seen comforting a Gambian national and UK resident who had tried unsuccessfully to get his family out.
Ebrima Jajne described the situation as "really scary for everybody... because this president (Jammeh) doesn't want to step down and people are fleeing."