A senior tribal government official was killed in a roadside bomb in Pakistan on Sunday as the country voted in by-elections to fill the parliamentary seat vacated by ousted Prime Minister Nawaz Sharif.

Fawad Ali, the assistant administrator, was traveling with the police to attend a meeting in the Bajur tribal region when their vehicle was struck by the device Sunday.

A Pakistani official added that four tribal police were also killed in the attack that took place near the Afghan border.

Anwarul Haq, another tribal official, said the device was detonated remotely, and that a search for the perpetrators is underway.

The Taliban later claimed responsibility for the attack.

Extremists have long operated in the tribal region along the Afghan border, where they attack security forces and those seen as cooperating with the central government.

In the by-elections, Sharif’s ruling Pakistan Muslim League-Nawaz (PML-N) party hopes a resounding victory in the eastern city of Lahore would show that support for the family was undiminished despite the Supreme Court’s removal of Sharif in July.

Sharif’s daughter Maryam has spearheaded the PML-N campaign for her mother Kulsoom – who is the MPL-N candidate despite receiving cancer treatment in London with Nawaz at her side.

Maryam, who some PML-N leaders see as a future leader, has framed the poll as a chance for voters to give a bloody nose to the judiciary by handing the party a thumping victory.

“Will you take revenge for your disrespected vote?” Maryam asked supporters at a recent rally.

Opposition leader Imran Khan – whose threats of street protests pushed the Supreme Court to launch a probe into Nawaz’s wealth – is seeking to build on the success of his anti-graft crusade by making inroads into Sharifs’ power base in Punjab.

The Supreme Court in July disqualified Sharif because he did not declare a monthly salary, equivalent to $2,722, from a company owned by his son when the veteran leader, who had held power twice in the 1990s, became prime minister for the third time. Sharif denies receiving the salary.

Analysts predict PML-N will win again but they say Khan’s party would build momentum ahead of the 2018 poll if PTI candidate Yasmin Rashid, a gynecologist from the area, substantially reduces the PML-N’s 40,000 vote-winning margin from 2013.