The King of Tonga has appointed a diplomat and former lieutenant colonel in the army, 'Aloua Fetu'utolu Tupou, as the new defence minister.
The portfolio was previously held by the Prime Minister and the king's youngest son, Prince 'Ulukalala Lavaka Ata.
A government statement gave no reason for the change.
Until recently, the prime minister had also been the foreign minister.
Last month, the ministers for justice, police and commerce were sacked amid apparent dissent over the government's airline policy.