UN chief António Guterres has demanded the immediate release of Mali’s President Bah Ndaw and PM Moctar Ouane, who have been detained by soldiers.
They were driven by soldiers to a military camp near the capital, Bamako.
The two men have been leading an interim government which took power after a military coup last August.
They were detained just hours after a government reshuffle in which two army officers who took part in the coup were replaced.
Late on Monday, Mr Ouane told AFP in a phone call that soldiers “came to get him”. The news agency said the line was then cut.
Defence Minister Souleymane Doucouré has also reportedly been detained.
The African Union, the Economic Community of West African States (Ecowas), the EU and the US have also condemned the arrests, saying Mali’s top politicians must be released without any preconditions.