One of Pakistan's most notorious gangsters, the alleged mastermind of a string of murders of local politicians and policemen, was arrested on Saturday in the country's crime-ridden commercial capital of Karachi.

"Lyari gang war leader Uzair Baluch has been arrested at outskirts of Karachi while entering the city," the Rangers paramilitary force said in a statement, with a photo showing him sitting handcuffed in a vehicle.

Baluch's criminal network controls much of Karachi's teeming Lyari slum. Local media have linked him to more than 20 cases of murder, extortion and terrorism and members of his gang have reportedly played football with the severed heads of his rivals.

The early morning arrest of Baluch, believed to be about 40 years old, surprised many who had thought he was already in custody after Interpol detained him in Dubai in 2014.

Karachi is Pakistan's largest and richest city, home to the central bank and stock exchange, a major port and some of the most violent areas of the country.

Many of its sprawling slums are split along ethnic lines, and political parties have been accused of backing armed groups that have carved the city into spheres of influence, a charge they deny.

Baluch's gang is believed to have been involved in killings of politicians from the influential MQM party, which critics accuse of racketeering, murder of opponents and holding the city to ransom by calling frequent mass strikes.

A major military operation, launched in 2013, is credited with slashing Karachi's murder and kidnapping rates. But the clampdown has drawn protests from opposition politicians who say their party members have been targeted, and activists who accuse security forces of widespread human rights abuses.-Reuters