The killing of school teacher Saleem Rida took place in Quetta market, in Quetta city, Baluchistan, Aljazeera's correspondent in Pakistan quoted the Quetta deputy police chief as saying on Monday.

Rida's wife was also injured in the attack.

Aljazeera's correspondent said Pakistani police had tightened security measures in Quetta city, fearing the eruption of sectarian violence, which has been steadily escalating. 

Second attack

Late on Sunday, in Karachi, armed men on a motorcycle opened fire at a car carrying the head of a Sunni religious school, injuring him and killing his 22-year-old son in a suspected sectarian attack, police said.

Nobody claimed responsibility for the attack and senior police official Athar Rashid Butt said officers were still investigating.

"Apparently it seems to be a sectarian attack, but we have opened investigations, and are looking into all aspects"

Police official

The injured cleric, Mohammed Ahmad Madni, 58, head of the Sunni school Jamia Mahmoodia, was going home with his son, Abdullah Madni, when assailants targeted his car. The son died at the scene, a police official said.

"Apparently it seems to be a sectarian attack, but we have opened investigations, and are looking into all aspects," he said.

The elder Madni is the brother of Maulana Azam Tariq, former head of the outlawed Sipah-e-Sahaba group, who was killed in a shootout near the capital Islamabad in 2003.

Tariq had made many enemies as head of his group, which was blamed for the killings of hundreds of minority Shia in recent years.

Most of Pakistan's Sunni and Shia Muslims live peacefully together, but small radical groups on both sides often target each other's leaders and activists.

About 97% of Pakistan's 150 million population is Muslim, and Sunnis outnumber Shia by a ratio of about four to one.