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TUNIS, Tunisia (AP) - Police have stepped up security in Tunisia's capital amid protests against the government marking three years since a young vendor set himself on fire, leading to revolutions across the Arab world.

The extremist Ansar al-Shariah movement, which has links to al-Qaida and is believed to have organized an attack on the U.S. Embassy, called for protests Tuesday at government headquarters in the Tunis casbah.

Police filled key intersections and checked cars entering downtown. Protesters denounced the media and counter-revolutionaries.

Tunisians overthrew a longtime dictator after an uprising sparked by the Dec. 17, 2010 self-immolation of vendor Mohamed Bouazizi. His act unleashed pent-up anger at corruption and repression.

The protests in Tunis and Bouazizi's hometown came days after the selection of a new prime minister amid a difficult transition to democracy.

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