Belaid, a prominent secular politician, was shot dead as he left his home Wednesday morning for work. No one has claimed responsibility for the attack.
Weeping Thursday beside his casket, his widow, Besma Belaid, was among those pointing the finger at the climate fostered by the governing Ennahda party, which is led by moderate Islamists.
"It's an open invitation to violence," she said. "I can only accuse this party."
Chokri Belaid had warned early this week that the government had given a green light to political violence.
A general strike called by trades unions for Friday, the first such action in Tunisia in three decades, closed many shops, cafes and other businesses. The national airline, Tunisair, warned of possible flight disruptions.
Protests have also erupted in the central towns of Gafsa and Sidi Bouzid, the birthplace of the revolution.
Support for Belaid went beyond his party, the secular-leftist Democratic Patriots. He was also the voice of a coalition of secular opposition parties known as the Popular Front and decried violence.
But Belaid routinely received death threats for his criticism of Tunisia's moderate Islamist-led government. He talked about the threats on his frequent television appearances but said he didn't fear for his life.
Official investigators have yet to reach a conclusion on who may have been responsible.
Amna Guellali, of the rights group Human Rights Watch, said the government itself bears some responsibility because of its "laxity" in failing to respond to a climate of rising political violence.
"We warned the government that these incidents of violence should be investigated thoroughly and that people who have perpetrated these acts should be punished ... but we haven't heard anything back," she told CNN in Tunis.
She cited calls by preachers in some mosques in July for the killing of certain Tunisian political figures and personalities, including Belaid, she said.
"We didn't see the government reacting to these calls of clear incitement to murder," she said. "A government has to protect its citizens ... especially if there are clear threats against this person."