Deadly violence has erupted in Karachi, Pakistan's biggest city, amid a continuing war of words between members of the country's ruling party and a locally powerful rival movement.

Up to 14 people were killed in riots which began on Wednesday, following a speech by Zulfiqar Mirza, Pakistan's provincial minister, in which he criticised Altaf Hussain, the founder of the Muttahida Qaumi Movement (MQM).

The MQM is the biggest party in Sindh province, of which Karachi is the capital, representing the families of Urdu speakers who left India for Pakistan in 1947.