Two Frenchmen were among several people arrested in Madagascar following a failed assassination attempt on President Andry Rajoelina.
Prosecutors said the arrests were made on Tuesday as part of an investigation into an attack on state security.
It's understood the men, named as dual Franco-Malagasy national Paul Rafanoharana and Frenchman Philippe François, have been charged with undermining state security.
Prosecutors say they have evidence of a plot to assassinate several high-ranking political figures, including the president.
The French nationals are both "Saint-Cyriens" - French cadet officers who trained at the French military academy of Saint-Cyr.
Rafanoharana is the head of an investment fund, while François is an adviser to the Archbishop of Antananarivo, Monsignor Odon.
Rafanoharana's name has recently been circulated as a potential prime minister in the event of a cabinet reshuffle.
According to an anonymous source, Rafanoharana was arrested by a dozen armed men at his home on Tuesday evening, while François was arrested in the departure lounge of Ivato airport as he was about to leave for France.Retired officers
During the country's independence celebrations on 26 June, the gendarmerie announced they had foiled an assassination attempt on their boss, who is also the president's right-hand man, General Richard Ravalomanana.
One of the poorest countries in the world, Madagascar has experienced many serious political crises over the past 20 years.