General Dario Caceres was sworn in the new army commander 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.
Paraguay’s defence minister said the changes were not politically motivated.
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.
The changes have provoked some discontent among former officers.
President Lugo warned last year that some in the military were plotting against him The former military chief, Admiral Cibar Benitez, who was sacked last year, told the Paraguayan newspaper ABC Color that the decision was an “abuse” and showed a “lack of respect” that would harm the armed forces.
But he said the military would not challenge its subordination to civilian control.
The BBC’s Valeria Smink, reporting from the region, says few observers believe there is a danger of a military coup in Paraguay – partly because the influence of the armed forces is much reduced.
Former bishop Fernando Lugo, 58, ended six decades of one-party government in Paraguay when he was elected in 2008 on a promise of reform.
From 1954 to 1989 the country was under the military rule of Gen Alfredo Stroessner, whose Colorado party remained in power until Mr Lugo’s victory.
The president – who is now receiving treatment for cancer – has since seen his popularity slump, reducing his chances of implementing reform in one of South America’s poorest and most unequal countries.
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