At least 24 people have been killed in the southern Pakistani port city of Karachi in violence since Saturday, police and hospital sources say.
Most violence was reported from the eastern and central parts of the city, police say.
Hundreds of people have been killed in ethnic violence in this sprawling metropolis in recent months.
Much of it has involved activists of the city’s dominant parties such as the MQM, the ANP and PPP.
The latest round of violence started when members of the Muttahida Quami Movement (MQM) resisted attempts by a breakaway faction to come out of hiding – after a decade under cover – and enter areas of the city.
The MQM is mainly a party of Muslim Urdu-speaking people whose families moved to Sindh province at the time of the partition of India in 1947.
The MQM(H) broke away from the MQM in 1991, and since then the two have had a history of mutual violence and armed hostilities.
The top leaders of MQM(H) were jailed in 2002-03 on various charges, and the bulk of its activists went into hiding, fearing persecution by members of the MQM who were then in power.
The MQM is still a part of the ruling coalition both at the centre and in Sindh province, of which Karachi is the capital.
The failure of the prosecution to obtain a conviction against Afaq Ahmad, the top leader of the MQM(H), prompted his party activists to return to their areas of the city.
Witnesses told BBC Urdu service that violence erupted in Malir district of Karachi on Saturday when some MQM(H) activists tried to enter the area. The activists were among those who had been in hiding for nearly 10 years after their leaders were jailed on various charges.
She said that the houses of three MQM(H) activists were also burnt down.
Meanwhile, the London-based chief of MQM party, Altaf Hussain, in a statement on Sunday blamed “armed terrorists” and “criminal elements” for causing a “bloodbath” in some areas.
Police and paramilitary rangers have been put on 24-hour patrol duty in some tense areas of Karachi, where weapons were recovered and arrests made, police official Naim Baroka told the media.
Meanwhile the administration has banned pillion riding on motorbikes to reduce the number of drive-by shootings.