(CNN) -- Pakistanis cast ballots in Karachi on Sunday, a day after the slaying of a well-known political leader who had accused rivals of vote rigging. As voters headed to polls, accusations flew over Zahra Shahid Hussain's death. Sources said an execution-style attack on the eve of the election killed Hussain, a senior vice president of the Tehreek-e-Insaf party, or PTI. The party made headlines after nationwide elections on May 11, alleging vote rigging in Karachi and elsewhere. Amid the allegations, election officials held a revote Sunday for one National Assembly seat and two Provincial Assembly seats in Karachi, Pakistan's largest city. Unofficial results from the country's election commission showed that PTI candidate Arif Alvi won the National Assembly seat.
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NEW: Family and friends bury Zahra Shahid Hussain
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The Pakistani political leader was killed outside her home in Karachi
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The rival MQM party denies responsibility and condemns the killing
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A revote is held in parts of Karachi after vote-rigging accusations
Meanwhile on Sunday, family, friends and members of the @placeholder party attended Hussain's funeral.