At least 12 people were killed and 25 wounded Wednesday by a blast outside a poll candidate’s office in southwestern Pakistan, officials said, on the eve of an election marred by violence and allegations of poll-rigging.

The attack occurred near the office of an independent candidate in Pishin district, around 50 kilometres (30 miles) from the city of Quetta and around 100 kilometres from the border with Afghanistan.

“Twelve people were killed while 25 others were injured,” a police official in Quetta who asked not to be named told AFP.

“The initial probe suggests that it was an IED (improvised explosive device) explosion, and the IED was placed on a motorcycle.”

Jan Achakzai, the caretaker information minister for the province, confirmed the death toll.

“It was an apparent IED blast that resulted in the death of 12 people and left more than 25 injured,” he said.

More than half a million security officers began deploying Wednesday, with authorities distributing ballot papers to more than 90,000 polling stations.

The election has been marred by allegations of pre-poll rigging following a crackdown on the party of jailed former prime minister Imran Khan, winner of the 2018 poll, but booted out of power by a national assembly vote of no-confidence four years later.

There have also been multiple security incidents in the run-in to Thursday’s vote, with at least two candidates shot dead and dozens more targeted in attacks across the country.

Campaigning officially ended on Tuesday night and voting is due to begin at 8:00 am local time (0300 GMT) Thursday, closing at 5:00 pm.

In Lahore, a stream of returning officers accompanied by police were seen collecting neon-green sacks of voting materials from a central distribution centre to take to their polling stations.

“The security set up is a lot better because the ECP (Election Commission of Pakistan) has installed its app and taken other measures,” said Mohammad Baqir, referring to electronic scrutiny of those collecting voting materials.

“The work is going smoothly.”

The figures are staggering in a country of 240 million people — the world’s fifth most populous — with around 128 million eligible to vote.

Nearly 18,000 candidates are standing for seats in the national and four provincial assemblies, with 266 seats directly contested in the former — an additional 70 reserved for women and minorities — and 749 places in the regional parliaments.

“We must ensure security measures at every level,” Sindh provincial police chief Rafat Mukhtar told a news briefing Wednesday in the port city of Karachi.