Zambia's President Michael Sata has gone abroad for a medical check-up amid persistent speculation that he is seriously ill.
Mr Sata's office said the 77-year-old leader flew out on Sunday but it did not disclose his destination.
Mr Sata made a rare public appearance last month to tell parliament: "I am not dead."
The BBC's Meluse Kapatamoyo says this is the first time the authorities have said he is seeking medical treatment.
Defence Minister Edgar Lungu has been named acting president.
Known as "King Cobra" for his venomous tongue, Mr Sata was elected Zambia's president in 2011.
It is unclear whether he will return by Friday to preside over celebrations to mark 50 years of Zambia's independence.
Mr Sata has not been seen in public since returning from the UN General Assembly last month, where he failed to make a scheduled speech, the AFP news agency reports.