Cameroon's President Paul Biya has reshuffled senior military staff, promoting the head of the Presidential Guard to a brigadier general from colonel and replacing commanders in four of the country's five joint military regions, according to three separate presidential decrees.

Biya, the world's oldest head of state, has been out of the public eye for two months. He left Cameroon on June 7 for what the civil cabinet described as "a brief private stay in Europe" and has not returned.

The decrees were signed on Monday and announced on national radio.

Cameroon's government spokesperson, Rene Emmanuel Sadi, did not respond to requests for comment. He told French broadcaster RFI on Sunday that "the president is alive" and will soon return.

The appointments included a new commander of the Rapid Intervention Brigade, the promotion of Major General Ebaka Hippolyte to Major General of the Armed Forces General Staff as well as several colonels to the rank of brigadier general, and changes to motorised infantry brigades.

Cameroon's ruling party called a rare meeting of senior leaders last month as criticism mounted over the continued absence of Biya.

Biya, 93, who has ruled the oil- and cocoa-producing country since 1982, often spends extended stretches abroad, though his advanced age has lately fuelled speculation about ​his health, whereabouts and ability to govern. The current overseas trip is one of his ​longest yet.