undreds of miles from their homeland in the mountainous northwest, Pakistani Taliban fighters have started to flex their muscles more forcefully in parts of this vast city, and they are openly taking ground.

Taliban gunmen have mounted guerrilla assaults on police stations, killing scores of officers. They have stepped up extortion rackets that target rich businessmen and traders, and shot dead public health workers engaged in polio vaccination efforts. In some neighborhoods, Taliban clerics have started to mediate disputes through a parallel judicial system.

The grab for influence and power in Karachi shows that the Taliban have been able to extend their reach across Pakistan, even here in the country’s most populous city, with about 20 million inhabitants. No longer can they be written off as endemic only to the country’s frontier regions.

In joining Karachi’s street wars, the Taliban are upending a long-established network of competing criminal, ethnic and political armed groups in this combustible city.