IMRAN Khan has claimed a political rival and the British Government must take responsibility for the assassination of a senior member of his political party.

An upmarket constituency of Pakistan's violence-plagued city of Karachi voted again under tight security yesterday, a day after gunmen killed a senior politician from a reformist party in the district and a week after general elections.

It was not immediately clear who killed Zara Shahid Hussain, a vice-president of the Pakistan Tehrik i Insaf (PTI) party of the former cricket star.

Mr Khan, the PTI leader, blamed the killing on the Muttahida Quami Movement (MQM), which has a stranglehold on the city. MQM leaders denied responsibility, con-demned the killing and demanded a retraction from Mr Khan.

The attack in the upmarket Defence area, the family neighbourhood of assassinated former prime minister Benazir Bhutto, capped a bloody election campaign in which around 150 people were killed nationwide.

Elections the previous Saturday delivered a landslide victory to opposition leader Nawaz Sharif and his Pakistan Muslim League-Nawaz (PML-N).

However, results from a handful of constituencies across the country are still uncertain amid accusations of vote-rigging. There is polling in a few others where security issues prevented voting.

The election gave the MQM 18 of 19 national assembly seats in Karachi, Pakistan's biggest city. The constituency, known blandly as NA-250, where the re-poll took place is thought to be a stronghold of the PTI.

The re-vote took place at 43 of 180 polling stations. The MQM, which wanted re-polling of the whole constituency, boycotted the vote.

Whatever the result, Mr Sharif's national landslide win is assured. However, as Pakistan's financial centre, Karachi generates around half of Government revenues and stability in the city is essential to the stability of the whole country.

For the first time, each ballot box was guarded by a ranger and a soldier inside and outside the booths to ensure security and no violence had been reported by early afternoon.

Police said three gunmen shot Ms Hussain on Saturday outside her home in Defence. "Her death has sent shockwaves across the rank and file of the party," Mr Khan said.

"I hold Altaf Hussain [the MQM leader] directly responsible for the murder as he openly threatened PTI workers and leaders through public broadcasts," Mr Khan, recovering in hospital from a fall during campaigning, added in a tweet.

"I also hold the British Government responsible as I had warned them about British citizen Altaf Hussain after his open threats."

Mr Hussain is accused of murder in Pakistan and leads his party remotely from exile in England. His party is designated a terrorist organisation by Canada, an accusation it strongly denies.

In recent days he gave a speech which many Pakistanis felt was an incitement to attack political rivals. British police are investigating whether it constituted a hate speech.

Mr Khan's election campaign galvanised many Pakistanis, pushing the PTI from a marginal party to Pakistan's third largest.

Karachi, the nuclear-armed country's key port, is home to 18 million people. It sees typically about a dozen murders a day, a combination of political killings, attacks by the Pakistan Taliban and sectarian militant groups, and street crime.