QUETTA, Pakistan — The death toll from a horrific bombing that tore through a crowded vegetable market in southwestern Pakistan climbed to 81 with many of the severely wounded dying overnight, a Pakistani police official said Sunday.

Police official Fayyaz Saumbal said 164 people also were wounded by the explosion Saturday in the city of Quetta just as people shopped for produce for their evening meal. The bomb was hidden in a water tank and towed into the market by a tractor, Quetta police chief Zubair Mahmood told reporters.

It was the deadliest incident since bombings targeting Shiites in the same city killed 86 people earlier this year, leading to days of protests that eventually toppled the local government.

Shiites have been increasingly attacked by militant groups who view them as heretics and non-Muslims in the country, which is dominated by Sunni Muslims. Many of the Shiites in Quetta, including those in the neighborhood attacked Saturday, are Hazaras, an ethnic group that migrated to Pakistan from Afghanistan more than a century ago.

The blast, which destroyed shops and caused a two-story building to collapse, left a massive crater where it exploded.

Mahmood said police did not yet know who was behind the bombing but a local television station reported that Lashker-e-Jhangvi, a Sunni extremist group that has targeted Shiites in the past, had called to claim responsibility.

Last year was particularly deadly for Shiites in Pakistan. According to Human Rights Watch, more than 400 were killed in targeted attacks across the country. The human rights group said more than 125 were killed in Baluchistan province, most of whom belonged to the Hazara community.

Rights groups have accused the government of not doing enough to protect Shiites in the country.