Police say Khursheed Anwar, general secretary of Tehrik-e-Jafria, was gunned down by two armed men in the city of Dera Ismail Khan, west of Lahore.

The incident has led to angry reaction from members of the religious group, and paramilitary frontier forces have been called out in the city to control the situation.

The BBC's Zafar Abbas in Islamabad: "A big hunt has been ordered for the killers"

Police say the attack took place in the morning, while Mr Anwar was driving his daughter to college in Pakistan's remote North West Frontier Province.

Two gunmen are said to have blocked his car and opened fire from automatic weapons, killing Mr Anwar, his daughter and the bodyguard.

Mr Anwar's wife and another bodyguard are reported to have been wounded in the attack, according to the Associated Press.

No one has claimed to have carried out the attack but police said they believe it is a case of religious sectarianism.

Violent reaction

Within minutes of the attack, Shia supporters took to the streets and chanted slogans against members of a rival Sunni group.

Several shops were ransacked and some were reported to have been burned down. Paramilitary forces have now fanned across the city to try and control the situation.

Sectarian violence between extremist groups of the majority Sunni and the minority Shia has led to more than 200 deaths in the past two years.

In January, 16 people were killed in a gun attack on a Shia mosque in the city of Multan, during the Muslim holy month of Ramadan.