Gunmen on a motorcycle have shot dead a prosecutor investigating the 2007 assassination of former Pakistani prime minister Benazir Bhutto.

Police sources said Chaudhry Zulfikar was killed as he left his home to attend a hearing in the case.

Mr Zulfikar was also the prosecutor investigating the 2008 attacks on India's commercial capital, Mumbai, in which 166 people were killed.

India said militants based in Pakistan were behind the three-day rampage.

Ms Bhutto's assassination is shrouded in mystery.

She was killed in a gun and suicide bomb attack after an election rally in the city of Rawalpindi, weeks after she returned to Pakistan from years in self-imposed exile.

A report by a UN commission of inquiry released in 2010 said any credible investigation should not rule out the possibility that members of Pakistan's military and security establishment were involved.

Ms Bhutto was a fierce critic of Pakistan's Taliban and Islamist groups that had been patronised by elements of Pakistan's military.

She was also deeply mistrusted by the security establishment.

The killing of the prosecutor comes days after a Pakistani court put former president Pervez Musharraf on a 14-day judicial remand over charges of failing to provide adequate security for Ms Bhutto before her assassination.

The former army chief has always denied responsibility for Ms Bhutto's death.

He returned to Pakistan in March after nearly four years of self-imposed exile to contest the 11 May general election.

He has since been banned from politics for life.