At least 21 people have been killed in a week of violence between rival political groups in the Pakistani city of Karachi, officials say. Seven of the dead were activists from Karachi's dominant political force, the Muttahida Qaumi Movement (MQM). The rest were political workers from a rival breakaway faction, the Muhajir Qaumi Movement, or Haqiqi group. The groups have a history of violence dating back to 1992 when the political movement split. There are fears the latest violence could escalate. The MQM has dominated politics in Karachi since the mid-1980s. It is part of the federal coalition which runs Sindh province, of which Karachi is the capital. It is led by Altaf Hussain who lives in exile in London. The party is mostly made up of and supported by Urdu-speakers known as Mohajirs, who migrated to Pakistan from India around the time of partition. The BBC's M Ilyas Khan in Islamabad says that since the MQM split in 1992, Mr Hussain's faction has retained the bulk of Karachi's Urdu-speaking voters. During its periods in power, it has strived to keep the top leaders of the MQM-Haqiqi behind bars on a series of charges, our correspondent says. The killings come shortly before a Karachi court is due to issue an order on the fate of several jailed Haqiqi group leaders. Karachi is Pakistan's biggest city, its commercial centre and has a long history of political, ethnic and religious violence. BBC NEWS | South Asia | Karachi political feud 'kills 21'