Ali Haider Gilani, the son of a former Pakistani prime minister, Yousuf Raza Gilani, was kidnapped by gunman at a political gathering on Thursday.
His secretary and guard were shot dead in the attack which happened as Ali Haider Gilani, who is running for a provincial assembly seat in the district of Multan, was headed to a political gathering in the central city of Multan, the Associated Press reported.
The Taliban denied responsibility in a telephone call to Reuters.
The latest violence, which has the potential to upset the country's historic election on Saturday, happened as a letter from the leader of the Pakistani Taliban, Hakimullah Mehsud, revealed plans for suicide bomb attacks on election day, Reuters reported.
In a message to the group's spokesman, he outlined plans for attacks in all four of the country's provinces on polling day on Saturday.
"We don't accept the system of infidels which is called democracy," Mehsud said in the letter, dated May 1, and obtained by Reuters on Thursday.
The kidnapping and threats of violence could affect voter turnout for Saturday's election, The Guardian wrote.
The family of Ali Haider Gilani announced they will boycott the election unless Haider is returned safely.
"If we don't get my brother by this evening I will not let the elections happen in my area," his brother, Musa, said in televised comments.
Haider was contesting a seat in the Punjab provincial assembly, while his two brothers were contesting seats in the national assembly.
The kidnapping has highlighted a serious lack of security in Pakistan ahead of election day. Many are worried militant attacks will affect the elections' outcome by sidelining less well-known candidates.
Mariya Karimjee reported from Karachi.