TUNIS — The funeral of a slain Tunisian opposition leader was marred Friday by clashes between police and gangs of young men destroying nearby cars, as black smoke spiraled from burning vehicles into the sky and clouds of tear gas floated over the nearby cemetery.

Hundreds of thousands of Tunisians chanting antigovernment slogans converged on the Jellaz cemetery for the funeral of Chokri Belaid, a left-wing politician whose assassination Wednesday outside his home has exacerbated Tunisia’s political crisis and escalated tensions in the North African nation that helped kick off the Arab Spring.