Pakistani police say gunmen killed at least 13 people early Tuesday in an apparent sectarian attack on a passenger bus carrying Shi'ite Muslims near the restive southwestern city of Quetta.
Police say unidentified gunmen on motorcycles ambushed the bus, lined up the passengers and opened fire on them. At least six people were wounded in the attack.
Authorites say at least 12 of those killed were Shi'ite Muslims, mostly from the Hazara ethnic community.
No one has claimed responsibility for the attack, which took place on the outskirts of Quetta, the capital of Pakistan's oil-rich southwestern Baluchistan province, bordering Iran and Afghanistan.
The area has seen a recent increase in attacks on the Shi'ite minority population by Sunni militants loyal to al-Qaida and the Taliban.
Following Tuesday's attack, a group of angry Shi'ite demonstrators staged a protest at the hospital where the victims had been taken, setting fire to the bus used to transport the wounded after it was emptied. Protesters also called for the Pakistani government to protect religious and ethnic minorities.
Last month near Quetta, gunmen carrying rocket launchers and Kalashnikovs attacked a bus bound for Iran, killing 26 Shi'ite Muslim pilgrims.
Pakistan has a Sunni Muslim majority, and although most Sunnis and Shi'ites coexist peacefully, extremists often target members of each community.
Last month, Amnesty International criticized the Pakistani government for failing to address a rising trend of sectarian violence. The rights group said that it had counted at least 15 attacks against Shi'ite minorities across Pakistan.
Some information for this report was provided by AP, AFP and Reuters.