Ghana is to deploy 205 soldiers to join the West African regional force to ensure the transition of power in The Gambia.
The Nigerian Air Force has already joined Senegalese troops on the border, who have said they are ready to enter the country if no political solution is reached by midnight.
A 90-day state of emergency has been declared in the country after its president of 22 years, Yahya Jammeh, has refused to hand over power after losing an election last year.
"The objective is to create an enabling environment ... [to] facilitate the inauguration of the President-Elect, Adama Barrow, on Thursday, January 19, 2017," Ghana's President Akufo-Addo said, referring to the winner of December's election.
- Video report by ITV News Africa Correspondent John Ray
Hundreds of Britons are to arrive back in the UK after being evacuated from The Gambia over fears for their safety.
Many more are still queuing in the airport waiting to be evacuated home after signs of growing political unrest.
Around 50-60,000 British tourists visit the West African nation each year.
The Nigerian air force say it has deployed to Senegal to "provide support in enforcing The Gambia's election mandate".
Gambia's president of 22 years, Yahya Jammeh, has refused to hand over power after losing an election last year.
Senegal troops are at the Gambian border and are understood to be ready to enter the country if no political solution is reached by midnight.
British tourists are being evacuated from the West African country.
Former Birmingham and Portsmouth midfielder Aliou Cisse has been appointed as the new head coach of Senegal.
The 38-year-old, who captained Senegal to the quarter-finals of the 2002 World Cup, succeeds Alain Giresse after the Frenchman departed following the Lions of Teranga's first-round exit from this year's African Nations Cup.
A tweet from the Senegalese federation's official account confirmed Cisse's appointment. Reports suggest the former Paris St Germain player has signed a four-year contract after stepping up from an assistant's role.
President Macky Sall of Senegal has appointed Justice Minister Aminata Toure as prime minister after sacking the previous government, Mr Toure told state radio.
"The president has asked me to form and lead a new government... I have accepted the job," she said.
Sall fired former Prime Minister Abdoul Mbaye a little more than a year after naming the former banker to head the government after he won a March 2012 presidential election.
President Obama has landed on African soil for only the second time in his presidency. Air Force One has touched down in the Senegalese capital of Dakar this evening.
He is travelling with first Lady Michelle Obama and daughters Malia and Sasha and will remain in Senegal for three days before travelling on to South Africa and Tanzania.
Obama's father was born in Kenya, and several of his relatives still live there, however the president spent just one day in Africa during his first four years in office.
Four people, including one French citizen have been killed in a suspected separatist rebel attack in Senegal's Casamance region, military sources have told Reuters.
Senegal's African Nations Cup tie with Ivory Coast was abandoned on Saturday when riot police fired teargas inside the packed stadium as thousands of fans lit fires and threw objects in protest at the home team's performance.
Five or six people were carried from the stadium on stretchers after the rioting while hundreds of Ivory Coast fans were huddled together on the field being guarded by police as clashes continued in the streets outside, said a Reuters eyewitness.
The referee halted the second-leg qualifying match with about 14 minutes to go and the visiting Ivorians 2-0 up thanks to two goals from former Chelsea striker Didier Drogba, the second from the penalty spot.
Both teams were then escorted out of the ground by security forces.
It is likely the result will stand but there was no immediate confirmation from the Confederation of African Football organisers.
Victory would send the Ivorians through to the finals in South Africa in January and eliminate Senegal.