Defeated Gambian leader Yahya Jammeh has agreed to cede power to the country's newly inaugurated leader, a Senegalese government official has confirmed.
Final arrangements were being made to the agreement, the official said.
Jammeh, however, has offered to step aside once before, but changed his mind.
But he was rapidly losing any claim to power, as the chief of Gambia's defence forces pledged his allegiance to the new president, Adama Barrow, and said Gambian forces would not put up a fight.
The leaders of Guinea and Mauritania arrived in Gambia earlier Friday to persuade Jammeh to cede power in the West African nation, while a regional military force awaited orders to roll into the capital and force him from the office he held for 22 years.
Barrow, who was elected president last month, was sworn in Thursday, and the UN Security Council voted unanimously to approve the regional military intervention.
His inauguration took place at the Gambian Embassy in neighbouring Senegal for Barrow's safety.
Defence forces chief Ousmane Badjie said that Gambia's security services all support Barrow and would not fight the regional force.
"You cannot push us to war for an issue we can solve politically," Badjie said. "We don't see any reason to fight."
With the security forces abandoning him and his Cabinet dissolved, Jammeh was increasingly isolated during the last-minute talks at his official residence in the capital, Banjul, with the Guinean and Mauritanian leaders.
The West African regional force, including tanks, moved in without facing any resistance, said Marcel Alain de Souza, chairman of the West African regional bloc, ECOWAS.
At least 20 military vehicles were seen Friday at the border town of Karang.
The regional force included troops from Senegal, Ghana, Nigeria, Togo and Mali, and they moved in after Barrow's inauguration and the UN vote.
Guinean President Alpha Conde was in Banjul with Mauritanian President Mohamed Ould Abdel Aziz.
Mauritania has been mentioned as a possible home in exile for Jammeh. After a first round of talks, they broke for Friday prayers and resumed.
Conde will offer Jammeh the chance to step down peacefully, de Souza said.
Jammeh "has the choice of going with President Alpha Conde," he said, but if that fails, "we will bring him by force or by will".
Jammeh had agreed to step down but demanded amnesty for any crimes he may have committed during his 22 years in power and wanted to stay in Gambia, in his home village of Kanilai, de Souza said.
Those demands are not acceptable to ECOWAS, he added.
In his inaugural speech, which took place under heavy security, Barrow urged Jammeh to respect the will of the people and step aside. He also called for Gambia's armed forces to stay in their barracks.
Some of Gambia's diplomatic missions began switching their allegiance.
"We embrace and support the new president Adama Barrow," said Almamy Kassama, an official at the Gambian mission to the African Union in Addis Ababa, Ethiopia, in an email.
Senegalese radio station RFM reported 30 Gambian soldiers had crossed into Senegal to fight alongside the regional forces.
"I think the Gambian military would know it's outnumbered," said Maggie Dwyer, an expert on West African armed forces at the University of Edinburgh. "Gambia's military has very little combat experience. This would be a very difficult situation for them."
She estimated it had 2,400 troops at most, plus fewer than 1,000 paramilitary forces.
"My guess is a very small number would actually put their life on the line for Jammeh," though some could stand by him to get the same deal he might receive to avoid prosecution, Ms Dwyer said.
Soldiers at checkpoints in Banjul appeared relaxed, with one telling visitors: "Welcome to the smiling coast."
African nations including South Africa continued stepping away from Jammeh, with the African Union saying the continental body no longer recognises him.
About 45,000 people have fled Gambia for Senegal, fearing violence, according to the Senegalese government and the UN refugee agency. About two thirds are children accompanied by women, the UN said.
Only about a few thousand international tourists are believed to still be in Gambia, and efforts continued to evacuate them.