Karachi politics has long been controlled by the Muttahida Quami Movement, the party representing migrants from what is now India.

WSJ: Karachi Beset by Political Strife

This violence also makes itself felt politically and there is profound antagonism between the local chapters of three political parties: the Pakistan People's Party (PPP), the mostly Pashtun Awami National Party (ANP) and the Muttahida Quami Movement (MQM).

BBC: How the Taliban gripped Karachi

Others have been casting doubts on the Muttahida Quami Movement (MQM) - the largest and most organised political party of the city which is a partner in power both at the provincial and central levels but whose relations with the ruling Pakistan People's Party (PPP) have soured over the past couple of months.

BBC: Karachi bomb was 'caused by IED'