By late afternoon, the center of the city was largely deserted and littered with stones, guarded by police armored vehicles and patrolled by a tank from the national guard. Knots of riot police chased protesters through the elegant downtown streets.
At least one policeman died in the clashes, the Interior Ministry said.
Protests flared across the rest of the country as well, with fierce clashes in the southern town of Gafsa and the coastal cities of Sousse and Monastir. Ennahda offices were also attacked in several towns, according to media reports.
Tunisian President Moncef Marzouki, a member of a secular party in the governing coalition, called the Belaid assassination a threat against all Tunisians in a speech before the European Parliament in Strasbourg before he rushed home, canceling a trip to Cairo.
"All these destabilization attempts — and there will be others because for some the Tunisian model should not succeed — I can tell you that we will face the challenge and defeat it," he told journalists.
The assassination also comes as Tunisia is struggling to revive its economy. On Monday, the central bank head, Chedli Ayari, said that while the country was on the road to recovery, the political squabbling had to be resolved to reassure foreign and Tunisian investors.
"This assassination is the gravest incident yet in a climate of mounting violence," said Eric Goldstein, deputy Middle East and North Africa director at Human Rights Watch. "Since Tunisia's revolution, there have been violent assaults against journalists, political activists, artists, and simple citizens, many of which the authorities did not investigate, let alone prosecute."
Several opposition parties suspended their participation in the constitutional assembly over the assassination and are now calling for a general strike, which could further inflame tensions. By Wednesday evening, however, they had yet to react to Jebali's announcement of a caretaker government.
Nejib Chebbi of the centrist Jomhouri Party warned prior to Jebali's announcement that other political figures could be targeted for assassination, and he called for the dissolution of the Leagues to Protect the Revolution.
The night before his death, Belaid had called for the dissolution of those leagues as well.
"There are groups inside Ennahda inciting violence," Belaid told the Nessma TV channel. He alleged that Ennahda leader "Rachid Ghannouchi considers the leagues to be the conscience of the nation, so the defense of the authors of violence is clear. All those who oppose Ennahda become the targets of violence."
Ennahda, however, has denied supporting any violence and promised an investigation into the assassination. Ghannouchi called Belaid's killing an "ignoble crime" and offered his condolences to his family.
As international condemnation of the assassination swiftly poured in, several countries expressed worry over the violence in Tunisia.
"There is no justification for an outrageous and cowardly act of violence like this," U.S. State Department spokeswoman Victoria Nuland told reporters. "There's no place in the new Tunisia for violence. We urge the government of Tunisia to conduct a fair, transparent and professional investigation to ensure the perpetrators are brought to justice, consistent with Tunisian and international law."
French President Francois Hollande also expressed worry. "This murder deprives Tunisia of one of its most courageous and free voices," he said in a statement.
Schemm reported from Rabat. Associated Press writers Raf Casert in Strasbourg, Sarah DiLorenzo in Paris and Bradley Klapper in Washington contributed to this report.
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