Hawzah News Agency (Dera Ismail Khan, Pakistan) - Sunday's attack targeted the vehicle transporting Ikramullah Gandapur, a member of the Pakistan Tehreek-e-Insaf (PTI) party led by cricketer-turned-politician Imran Khan, in the city of Dera Ismail Khan.
District police chief Zaheer Afridi said Gandapur died of injuries in the Combined Military Hospital.
Video images from the scene showed three bleeding, unconscious passengers inside the badly damaged Toyota Land Cruiser.
Faraz Mughul, Gandapur's assistant, confirmed the casualties.
Meanwhile, Imran Khan condemned the "cowardly terrorist attack" in a posting on Twitter.
In 2013, Gandapur's brother Israrullah, who was then the provincial law minister, was killed in an attack on his home.
The Sunday bombing is the latest in a number of attacks targeting politicians campaigning ahead of the elections, scheduled to be held on July 25.
On July 13, a blast in the southwestern province of Balochistan killed nearly 150 people .
At least 22 people were killed in a bombing on an anti-Taliban political event held in northwestern Pakistan on July 10. The blast targeted a campaign event held in the city of Peshawar organized by the Awami National Party (ANP), which has been targeted in the past over its opposition to militant groups such as Taliban.
Nearly 106 million Pakistanis will be eligible to cast their ballots in the elections.
The military has warned of threats ahead of the elections and said it would deploy more than 370,000 soldiers for security on the election day.
Despite frequent offensives by the Pakistani army, acts of terror by militant outfits continue to target security forces as well as civilians.
Thousands of Pakistanis have lost their lives in bombings and other militant attacks since 2001, when Pakistan entered an alliance with the United States in Washington’s so-called war on terror.