President Fernando Lugo of Paraguay has dismissed the heads of the army, navy and air force, as well as five other senior officers. It is the fourth time he has replaced the military's top commanders since he took office in 2008. The sacked commanders were only appointed last November after their predecessors were fired amid rumours of a coup plot. A statement from the armed forces announcing the changes did not explain why they were being made. But Paraguay's Defence Minister, Gen Cecilio Perez Bordon, later said they were aimed at institutionalizing the structure of the armed forces. The overall commander of the armed forces, Gen Oscar Velazquez, who was appointed by President Lugo last year, remains in his post.