ISLAMABAD, Pakistan — The death toll in a suicide bombing that targeted an election campaign event in southwestern Pakistan rose to 128 on Saturday, the deadliest terror attack in the country this year.

The attack, which took place on Friday in the restive province of Baluchistan, has renewed concerns that violence could disrupt national elections scheduled for July 25.

Pakistan is preparing for its second democratic transition after military rule, but a number of terrorist attacks targeting candidates and a growing sense of political unrest and turmoil threaten to undermine the credibility of the election.

Four such assaults have struck in the past week alone, with two candidates among those killed.

The federal government announced a day of mourning after the latest blast, with national flags at half-staff in all government buildings in Baluchistan, where two days of mourning were decreed. The Islamic State has claimed responsibility for the attack on Friday.