President Fernando Lugo of Paraguay has dismissed the commander of the armed forces, a day after he sacked the heads of the army, navy and air force.
It is the fourth time he has replaced the military's top commanders since he took office in 2008.
President Lugo said the changes were a "routine leadership renewal".
But critics have accused him of promoting younger officers to ensure the armed forces are loyal to him and his programme of political reform.
The sacked commanders were only appointed last November after their predecessors were fired amid rumours of a coup plot.
The armed forces chief Gen Oscar Velazquez has been replaced by Gen Benicio Melgarejo, who is the head of the president's security cabinet.
The changes have provoked some discontent among former officers.
The former General Bernadino Soto Estigarribia - now an opposition politician - accused Mr Lugo of "tampering" and "inflicting successive blows on the institutionality of the armed forces".
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.