Violence in Pakistan's largest city of Karachi claimed at least 15 more lives Sunday, bringing the death toll from three days of ethnic and political clashes to at least 40.

Sindh provincial authorities imposed an indefinite ban on motorcycle riding in the southern port city, saying many people have been killed in drive-by shootings.

Police reported shootings in several districts of the city of 18 million. Sindh police chief Wajid Durrani said police arrested 17 suspects; he blamed land speculators for igniting the unrest.

In Pakistan's northwest, a suicide bomber blew himself up at an army checkpoint in the Chag Malai area of South Waziristan, killing one soldier and wounding several others. A guard shot the suspect as he approached the checkpoint but he managed to detonate his explosives.

The Pakistani military launched operations in the tribal area more than a year ago with the goal of rooting out Pakistani Taliban militants based there. South Waziristan is a known stronghold for the group.