“According to the evidence in our possession, these individuals had devised a plan for the elimination and neutralization of a number of people including the head of state,” the attorney general said in a statement.
It added that investigations were under way and further details could not be disclosed. The arrests were made on Tuesday.
The extent of the plot, or how far advanced, was not immediately clear.
The statement did not specify the nationality of the foreign nationals.
A separate statement by the public security minister on Wednesday said that six people had been arrested: one foreign national, two binationals, and three Madagascan nationals.