Imran Khan blames MQM's Hussain for Karachi killing
Imran Khan, the leader of Pakistan's PTI party, has blamed one of his political rivals for the killing of PTI vice-president Zahra Shahid Hussain.
She was shot dead outside her home in Karachi by gunmen on a motorcycle.
On his Twitter feed, Mr Khan said he was holding the leader of Karachi's dominant MQM party, Altaf Hussain, responsible for her death - a claim the MQM has strongly denied.
It came as Karachi voted in a partial re-run of Pakistan's general election.
Police are investigating whether Mrs Hussain's killing was the result of an attempted robbery or a politically motivated murder.
Her funeral will take place later on Sunday at a mosque in Karachi.
Doctors at Karachi's Jinnah Hospital have told the BBC their initial examination showed two bullet marks on her body.
A full post-mortem report is expected within 24 hours.
Mr Khan said Mr Hussain, who is in self-imposed exile in London, had "openly threatened PTI workers and leaders through public broadcasts".
He said he was also holding the British government responsible, as he said he had warned them about Mr Hussain.
Mr Khan tweeted his accusations from his hospital bed, where he is recovering from a back injury sustained during a fall at an election rally in Lahore.
Last week, police in London confirmed they were investigating complaints that Mr Hussain had broken UK laws by issuing threats in a speech he made the day after the vote.
In response to accusations of electoral fraud, he is alleged to have threatened his accusers with violence.
Mr Hussain says that his remarks were taken out of context.
He has lived in the UK since 1991, saying his life would be at risk if he returned to Pakistan.
Sunday's electoral re-run in Karachi was ordered after Mr Khan's party accused the MQM of widespread vote-rigging and intimidation.
The MQM - which took most of the seats in Karachi in the original vote - denied any irregularities and boycotted the vote, which took place under tight security.
Voter turnout appeared slow but steady, says the BBC's Shahzeb Jillani, in Karachi.
The PTI is hoping to win the vote and make inroads in Pakistan's commercial capital, our correspondent adds.
Whatever the outcome of the re-run, it will not overturn the result of last week's vote, in which conservative leader Nawaz Sharif secured an unprecedented third term in power.
The MQM is seen as a perpetrator - as well as a victim - of violence in Karachi, our correspondent says.
Since the 1980s, it has won every election it has contested there.
But it also stands widely accused of ruling Karachi by fear and through vote-rigging, our correspondent says.
The general election on 11 May marked the first transition of power from one democratically elected government since the creation of the state of Pakistan in 1947.
However, the campaign was marred by violence in which about 150 people were killed across the country.
Mrs Hussain was shot by gunmen on a motorcycle outside her home in Karachi's upmarket Defence area, the family neighbourhood of assassinated Prime Minister Benazir Bhutto.
The MQM (Muttahida Qaumi Movement) is supported mainly by Muslim Urdu-speaking people whose families moved to Sindh province at the time of the partition of India in 1947.
Voting in Karachi on 11 May was disrupted by a bomb attack outside the office of the ANP party, in which 11 people were killed and more than 40 injured.
The bombing happened in the Landhi district of Karachi, where Taliban militants are known to be active.