@Mbuhari message to Nigerian after 51 days vacation.

Muhammadu Buhari‏ @MBuhari

"My message to you: I'm glad to be back home, & grateful for your prayers. The best way to repay you is to rededicate myself to serving you."

President Muhammadu Buhari on Friday returned to Nigeria after nearly two months' medical leave in Britain but did little to quell fears about the state of his health by saying he would not start work again immediately.

Vice-President Yemi Osinbajo would remain in charge at least over the weekend, he added.

Buhari, who looked gaunt in a billowing black kaftan, did not specify when he would resume his duties but his spokesman, Femi Adesina, said his return would be formalised on Monday.

He will write a letter to the National Assembly on Monday, Adesina said in a tweet, adding: "That makes his return to work formal, and constitutional."

Buhari's unspecified illness has been an increasing source of speculation in Nigeria ever since he left for London on January 19 for medical tests during a period of annual leave.

Aides had to counter persistent rumours online that he was seriously ill or even dead, despite a series of photographs showing him meeting senior Nigerian politicians.

On Thursday he was shown in photographs looking painfully thin at a meeting with the most senior cleric in the Anglican congregation, Archbishop of Canterbury Justin Welby.