Tunisian President Beji Caid Essebsi has been taken to hospital after suffering a “severe health crisis”, officials say.
They gave no further details. Mr Essebsi, 92, was also treated in hospital last week.
He became president of the North African nation after winning the first free elections in 2014, following Arab uprisings across the region.
Mr Essebsi is currently the world’s oldest sitting president.
Earlier this year, he announced he would not stand in elections expected in November, saying someone younger should take charge.
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Former President Zine el-Abedine Ben Ali was ousted in 2011 after 23 years in office.
Since then, Tunisia has won praise as the only democracy to emerge from the revolutions of the so-called Arab spring.
However, in recent years the country has suffered attacks by Islamists and economic problems, with unemployment a persistent issue.