Policeman killed in Karachi strike

A number of buses were set alight by protesters

A policeman has been killed in a bomb explosion during a strike in Pakistan's southern port of Karachi.

Police said the bomb went off in the back of a police vehicle - apparently as it was being taken away.

Police and army units were out in force

Three other policemen were wounded.

The strike closed down most shops and businesses and the streets were deserted.

Police say at least two people died in violence overnight ahead of the strike, which was called over water shortages.

The killings took place when unknown gunmen fired on two buses in different parts of the city.

Dozens of buses were also set on fire.

Police and army units were said to be patrolling the city in force.

Despite the security precautions, an early morning bomb blast injured two people.

"A small bomb was placed under a parked car and that car was totally destroyed," a policeman said.

Water shortages

The strike was called by the Muttahida Quami Movement - mainly composed of Urdu-speaking immigrants from India - and the Sindhi nationalist group, Jiye Sindh Quami Mahaz.

They are protesting against alleged police brutality during earlier demonstrations against shortages of irrigation water in Sindh province.

Drought has led to provincial disputes

At a time of severe drought, the groups say Pakistan's most populous province, Punjab, is taking too large a share of the country's resources.

Hundreds of activists are reported to have been detained in recent months for attending protests highlighting the water problem.

Police have used batons and tear gas to disperse the protests in line with the military government's ban on political gatherings.