TUNIS, Tunisia (AP) — A Tunisian investigative judge has ordered that influential Islamist leader Rached Ghannouchi remain in custody, his party said Thursday on its official social media.

The Ennahdha party denounced in a statement on Facebook the “unjust imprisonment” of its leader, after Ghannouchi was arrested by police Monday. On its English-language Twitter account, the party said Ghannouchi has been charged with conspiracy against state security and ordered to be imprisoned pending trial.

Ghannouchi’s lawyer Mokhtar Jemai confirmed his client was being detained Thursday.

Ennahdha said it was a “political measure” that aims to “cover the bitter failure of the power to improve the economic and social situation and the daily lives of the people.”

The National Salvation Front, the main opposition coalition that includes Ennahdha, said in a statement that Ghannouchi’s detention shows “the deterioration of freedoms in Tunisia.”

Ghannouchi, 81, is the most prominent critic of President Kais Saied. He served as speaker of Tunisia’s parliament until Saied dissolved the body last July and seized most executive powers in the North African country — a move that Ghannouchi and other opponents call a coup.

He has been detained for questioning a number of times in the past, but the circumstances of his latest detention suggested that this time was more serious.

Tunisia’s official TAP news agency reported earlier this week that he was detained on a warrant by counterterrorism prosecutors as part of an investigation into recent “provocative” comments. It did not elaborate.

Other Tunisian media reported that Ghannouchi was to be questioned over a video circulating online in which he purportedly says that the president’s perceived efforts to “eradicate” Islamist opposition threaten to unleash civil war.

The move comes amid growing social tensions and deepening economic troubles in Tunisia, the birthplace of the Arab Spring pro-democracy movement more than a decade ago.