The Fiji Military Forces say they detained lawyer, Ratu Savenaca Komaisavai, because he allegedly made comments against a lawyer working with the military.
Mr Komaisavai was taken to the Queen Elizabeth Barracks by soldiers on Saturday afternoon.
The Fijilive website reports the military spokesperson, Major Neumi Leweni, is saying that the statements made by Komaisavai are false.
Mr Leweni would not say what these statements were.
He says Mr Komaisavai is still being held at the barracks, adding he does not know when he will be released.