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.