Gunmen and arsonists have gone on the rampage in Pakistan's financial capital Karachi, killing at least eight people and setting dozens of vehicles alight, officials say.
The unrest was sparked by the murder of a political party worker and his brother late on Monday, reviving fears that the city of 18 million could return to horrifying levels of violence that left more than 1700 people dead last year.
Violence is a major concern in Karachi, the economic powerhouse of Pakistan whose Arabian port is used by the United States to ship supplies to the war in Afghanistan, although Pakistan has blockaded the border for four months.
Mansoor Mukhtar, 37, a member of the Muttahida Qaumi Movement (MQM), the largest political party in the city, was shot dead late on Monday when gunmen burst into the home where he was sleeping, police said.
His brother also died and his sister-in-law was wounded in the attack in the central neighbourhood of PIB Colony, police said.
Soon afterwards, armed men took to the streets and started setting fire to vehicles, in violence that left a further six people dead and more injured.
"Our hospitals have received a total of eight bodies of victims from today's firing incidents. They include an MQM member and his brother," said police surgeon Hamid Parhiar in the southern province Sindh, of which Karachi is the capital.
At least 38 vehicles, including buses, mini buses and trucks were torched in Karachi, senior official Roshan Sheikh said.
The MQM, which represents the Urdu-speaking majority and sits in President Asif Ali Zardari's governing coalition, denied any responsibility.
"We have been keeping Karachi peaceful for a long time and such incidents have been perpetrated by those who don't want to see our country stable and peaceful," party spokesman Wasay Jaleel told AFP.
The Human Rights Commission of Pakistan said 1715 people were killed in sudden flare-ups of violence in the city last year.
Officials documented more than 100 deaths in one week alone in October in what was Karachi's worst ethnic and political unrest in 16 years.
The violence has been linked to ethnic tensions between the Mohajirs, represented by the MQM, and Pashtun migrants from Pakistan's northwest affiliated to the Awami National Party (ANP).