The PML has 15 members in the 109-member Sindh Assembly and was able to form a regional government with the support of MQM, which has 28 seats in the legislature. With the backing of some fringe groups, the PML was commanding the support of 70 members in the House.

The MQM took this decision on Thursday evening after Sharif accused the party of being behind the killing of Hakim Saeed, the head of the Hamdard Foundation, and asked the party to hand over the culprits within three days.

Sharif told newsmen that he had given the ultimatum at a meeting with MQM leaders in Karachi on Wednesday night and had told them that ifthey did not hand over the suspects believed to be behind the murder, the prime minister's ruling PML-N party would be forced to break its alliance with the MQM.

This statement by the prime minister came as a surprise amidst allegations by the opposition that the Pakistan prime minister was shielding his coalition partners from being caught for the murder of Hakim Muhammad Saeed. Unidentified gunmen shot and killed Saeed, 78, of the Hamdard Dawakhana, on October 17 outside his clinic in Karachi.

Saeed, who migrated from Delhi in the fifties, set up the Hamdard Dawakhana in Pakistan on the lines of the Hamdard organisation in India, which is headed by his elder brother.

Sharif told newsmen in Karachi that the MQM was involved in the murder of Saeed, a former provincial governor. The Pakistan prime minister said that he was fully satisfied that the investigations into the murder were ``going in the right direction.'' He said that suspects picked up by the police had confessed to the crime and that thefinger pointed towards the MQM and its members. Previously, the MQM had broke away from the PML-N party in July and had threatened to sit in the Opposition based on which the prime minister had personally come to Karachi to bring back the party to the folds of the ruling alliance. After the PM's efforts, the MQM had decided to sit in the treasury benches but not be part of the government, a unique arrangement in Pakistan's parliamentary history.