At least eight members of Pakistan's ethnic Hazara minority have been killed and two people wounded, when unknown gunmen opened fire at a bus in a market in the outskirts of Quetta in Balochistan.

The men were returning from a vegetable market when four gunmen riding two motorcycles intercepted the bus and attacked it.

Hundreds of Shia Hazaras have been killed in bomb attacks and shootings in southwestern Balochistan in the last few years. Most of these attacks have been perpetrated by Lashkar-e-Jhangvi in Quetta.

Due to the history of the attacks, police have usually been providing them with security when they go shopping in the main fruit and vegetable market in the city of Quetta.

"An armed person barged into the bus and opened indiscriminate firing, killing at least eight people," Aitzaz Goriya, Senior Superintendent of Police Operations, told Al Jazeera.

"Police daily escort these vegetable vendors belonging to the Hazara community but today they didn't inform us before leaving to buy vegetables from Hazar Ganji, an area that is considered unsafe for them."

No one immediately claimed responsibility for the attack and no arrests have been made so far.

'Targeted operation'

Al Jazeera's Kamal Hyder, reporting from Islamabad, said automatic weapons were used on the bus carrying only Hazaras.

"According to police it appears to be a targeted operation at the Hazara community. The attack is likely to heighten tensions as the Shia community commemorates the month of Muharram beginning in less than two days and security forces will be on high alert," Hyder said.

Police and paramilitary Frontier Corps have launched a search operation in adjacent areas.

The dead and the injured have been taken to Combine Military Hospital for treatment.

According to the Human Rights Commission of Pakistan, as many as 200,000 Hazaras have fled to other cities or abroad.

More than 800 Shias have been killed in attacks in Pakistan since the beginning of 2012. Shia Muslims make up about a fifth of Pakistan's population.

Two other deadly attacks were carried out in Quetta on Thursday.

A prominent leader of the conservative Jamiat Ulema e-Islam party, Fazlur Rehman, survived a suicide attack on his convoy just as he was leaving a rally that he addressed. 

At least three people were killed and nine others wounded in the attack that badly damaged Rehman's bomb proof vehicle.

The third attack was a roadside bomb that killed another two people in the city.