The Pakistani prime minister, Nawaz Sharif, has accused a group of militants belonging to the MQM, the government's main coalition partner in Sind province, of the murder of a leading social reformer, Hakim Mohammad Saeed.

He was killed in an armed attack last week.

One of those accused of the attack is a provincial assembly member, Zulfiqar Haider.

Mr Sharif said that if the MQM leadership failed to hand over the eight accused, their political alliance would fall apart.

The MQM has strongly denied the accusation.