Muttahida Qaumi Movement (MQM), an ally of the ruling Pakistan People's Party(PPP), wanted the referendum to highlight people's sentiments against the Taliban, but has now postponed it in the wake of the holy month Muharram.

"Our co-ordination committee has decided to further extend the date of the referendum in respect of the month of Muharram," said an MQM statement after the referendum was postponed for a second time.

The party did not provide a future date for the poll, which had originally been scheduled for November 8 but was first delayed because of a defence products' exhibition in Expo centre Karachi.

MQM has been openly critical of the Pakistani Taliban, and earlier this month the militants threatened to attack the party. But MQM denied that the activity was being postponed due to the threats.

"This is not true that the referendum is being delayed because of the recent threats," Wasay Jalil, a spokesman for the party told AFP.