The 81-year-old head of the Islamist Ennahda party was summoned to meet the terrorism police on Tuesday and questioned from 5:00 p.m. until 6:00 a.m. on Wednesday, his lawyer Samir Dilou said.
Ghannouchi and another senior Ennahda figure, former prime minister Ali Laareyedh, were both initially summoned on Monday. Laareyedh was questioned through Monday evening and night and detained. Ghannouchi waited for 12 hours before being questioned.
Both men, and Ennahda, deny the accusations the police are investigating, that they helped Tunisian jihadists travel to Syria during the Islamic State crisis a decade ago. They will face a judge later on Wednesday, Dilou said.
Both accuse police of using the investigation to intimidate them because of the party's opposition to President Kais Saied's seizure of broad powers and shutdown in July 2021 of the elected parliament.
The police or other authorities have not commented on the case.
Ghannouchi was also investigated earlier this summer regarding accusations of money laundering, which he denied.
President Saied's critics accuse him of a coup for seizing most powers last year and moving to one-man rule, and of dismantling the democracy won in the 2011 revolution that triggered the Arab Spring uprisings
Saied says his actions were legal and necessary to save Tunisia from years of political paralysis. In July he passed a new constitution ratifying his expanded powers through a referendum.
Last week, he issued a decree mandating prison terms of five years for people spreading what he called false information online, a move that rights groups and the main journalists' union have said will undermine free speech