In a video message released today, Khan, who is under treatment at the Shaukat Khanum hospital in Lahore after an accident during the election campaign, said as soon as he was well he would himself lead the protests in Karachi.
"I regret that I would not be able to join the protest demonstrations in Karachi right now, but hopefully I will be rubbing shoulders with you as soon as doctors discharge me from the hospital", he said in his message.
60-year-old Zahra was shot by two unidentified men outside her home in Defence Phase IV.
Khan appealed to his party workers to stand fast against the brutalities, come what may.
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"Zahra Shahid Hussain did not lay down her life for nothing. Her sacrifice will not go in vain", he said.
Khan said that Karachi was being controlled by mongering fear among people and his workers should be prepared to fight this.
The Mutthaida Qaumi Movement (MQM) lashed out strongly at Imran for holding Altaf Hussain directly responsible for the murder of Zahra and said he had displayed his political immaturity.
MQM senior leader Farooq Sattar said the party would be filing defamation cases against Khan in the courts.
Meanwhile, a low turnout was witnessed in the re-polling at 43 polling stations in Karachi today in a constituency where the PTI candidate was in a strong position to win the National Assembly seat.