Police locked down a large area of central Tunis on Saturday, blocking roads as thousands of protesters, backed by the country's powerful labor union, gathered in Tunisia's biggest demonstration for years.
The rally was held to mark the anniversary of the 2013 killing of a prominent activist and to protest against police abuses that demonstrators say have imperiled the freedoms won in the 2011 revolution that triggered the "Arab spring."
Riot police deployed cordons around the city center, stopping both cars and many people from entering the streets around Avenue Habib Bourguiba as thousands of people gathered, a Reuters witness said.
Unlike previous marches in the wave of street protests that have rippled across Tunisia in recent weeks, Saturday's rally was backed by the UGTT union, the country's most powerful political organization with a million members.
Protests, which began last month with clashes and rioting in deprived districts over inequality, have increasingly focused on the large number of arrests, and reports - denied by the Interior Ministry - of abuse of detainees.
Mohammed Ammar, a member of parliament for the Attayar party, said he had phoned the prime minister to protest against the closure of central Tunis.
Protesters chanted slogans against the moderate Islamist Ennahda party, a member of successive government coalitions, and reprised the Arab Spring slogan: "The people want the fall of the regime."
A decade after Tunisia's revolution, its democratic political system is in crisis, mired in endless squabbling between the president, prime minister and parliament while the economy stagnates.
While some Tunisians, disillusioned by the fruits of the uprising, are nostalgic for the better living conditions they remember from the days of autocracy, others have decried a perceived erosion of the freedoms that democracy secured.
For some, the febrile climate has recalled the political polarization after a suspected hardline Islamist assassinated secular activist and lawyer Chokri Belaid in February 2013.
His death triggered a wave of mass protests in Tunisia that led to a grand bargain between the main Islamist and secular political parties to stop the country sinking into violence.