What do we know about the mutiny?
It is led by Col Malick Diaw – deputy head of the Kati camp – and another commander, Gen Sadio Camara, BBC Afrique’s Abdoul Ba in Bamako reports.
After taking over the camp, the mutineers marched on the capital.
In the afternoon they stormed Mr Keïta’s residence and arrested the president and his prime minister – who were both there.
The reason for the move is unclear, as is the number soldiers taking part in the mutiny. Some reports say it was fuelled by a pay dispute.
Kati camp was also the focus of a mutiny in 2012 by soldiers angry at the inability of the senior commanders to stop jihadists and Tuareg rebels taking control of northern Mali.
Footage from AFP news agency showed a building owned by the justice ministry in Bamako ablaze on Tuesday.
Shades of 2012
Analysis by Will Ross, BBC World Service Africa editor
What began as a mutiny appears to have morphed into a coup. This will be welcomed by the huge number of protesters who have been out on the streets for months calling for President Keïta to step down.
Parallels will be drawn between these events and 2012 when the government’s mishandling of a rebellion led to another coup.
Violent jihadists took advantage of that chaos to seize northern Mali. And they continue to cause havoc across the region.
Why is the president unpopular?
Ibrahim Boubacar Keïta won a second term in elections in 2018, but there is widespread anger over corruption, the mismanagement of the economy and the worsening security situation with jihadist and communal violence on the increase.
In recent months huge crowds led by populist imam Mahmoud Dicko have been calling on President Keïta to step down.
Much smaller crowds reportedly gathered in the capital on Tuesday in support of the soldiers.
What has the reaction been?
The chairman of the African Union Commission, Moussa Faki Mahamat, said in a tweet that he “emphatically condemns” the arrests of President Keïta and his prime minister.
The Economic Community of West African States (Ecowas) urged the mutineers to return to barracks.
“This mutiny comes at a time when, for several months now, Ecowas has been taking initiatives and conducting mediation efforts with all the Malian parties,” its statement said.
France’s Foreign Minister Jean Yves Le Drian also condemned “in the strongest terms this serious event” and he too urged soldiers to return to barracks.
Earlier the French embassy in Bamako posted a tweet “strongly” advising people to stay at home. France has troops in the West African state to fight militant Islamists.