KARACHI, Pakistan (AP) _ A mob demanding the release of a jailed legislator beat a policeman to death Friday and 12 people were wounded when riot police later opened fire to disperse the demonstrators.

Senior police officers, who according to official policy could not be identified, said police opened fire with rifles and shotguns several times and also used tear-gas grenades to disperse the crowd.

Hospital officials said 12 people were being treated for gunshot wounds.

The violence began when about 500 members of the Mohajir ethnic group, calling for the release of one of their leaders held in a Karachi jail, marched through the Liaquatabad district, set fire to a bus and blocked a main road.

When a van of police officers arrived, protesters attacked it with rocks and pulled one officer from the vehicle before it drove away. Witnesses said some members in the mob beat the officer to death.

Hospital officials, speaking with the condition they not be identified, confirmed that a policeman had been fatally beaten.

Riot police units then were sent to the area to reopen the road and disperse the protesters, who set fire to barriers as they fled. No arrests were reported immediately.

Mohajirs are Moslems who lived in India and fled to Pakistan after Britain granted the subcontinent indpendence in 1947 and divided the former colony into Moslem Pakistan and predominantly Hindu India.

At least 200 people have been killed over the past two months in clashes between Mohajirs and police and other ethnic groups in Karachi.

The Mohajirs are demanding the release of Afaq Shahid, one of their leaders and a member of the National Assembly imprisoned on charges of possessing explosives.

They also claim that Pakistan's other ethnic groups discriminate against them.