The main opposition party in Tunisia, Ennahda, has condemned the imprisonment of its leader as politically motivated.
A judge ordered the jailing of Rached Ghannouchi – a prominent critic of President Kais Saied – early on Thursday.
Mr Ghannouchi was arrested on Monday, accused of plotting against state security and making “inciting statements’.
Ennahda said his detention would not resolve Tunisia’s crippling crisis.
This week, the authorities banned the party from holding meetings and closed the headquarters of the main opposition coalition, the Salvation Front.
The US said the Tunisian leader’s latest actions represented a troubling escalation.
Mr Ghannouchi was the speaker of the Tunisian parliament until it was abolished by President Saied in 2021.