At least three people were killed in an improvised explosive device (IED) blast in Pakistan's northwestern Khyber Pakhtunkhwa province, police said on Wednesday.

The blast occurred in the Bajaur district of the province, killing the three people on the spot, including a former member of the Senate.

The police said that scores of people gathered for the campaign for the upcoming by-polls in the district when the roadside-planted bomb exploded.

An investigation has been launched to find the motives behind the incident. No group or individual has claimed responsibility for the attack yet.