Myanmar's civilian president, Htin Kyaw, has resigned with immediate effect "in order to take rest from the current duties and responsibilities", his office said in a statement posted on Facebook on Wednesday.
Htin Kyaw, whose post is largely ceremonial, has been a close ally of the country's de facto leader, Aung San Suu Kyi.
He was handpicked by the Nobel peace prize laureate to become president because a constitution drafted by the country's former junta bars her from the top office.
According to Reuters, there has been speculation in the local media for some months that Htin Kyaw was in ill-health, but this was denied by officials.
The president's office said: "According to the Myanmar constitution article 73 (b), procedures will be undertaken to fill the president vacancy within seven working days."