The son of Pakistan's slain former prime minister, Benazir Bhutto, launched his political career Thursday, vowing to continue his mother's fight for democracy.

In a speech marking the fifth anniversary of the leader's death Thursday, Bilawal Bhutto Zardari said his Pakistan People's Party pledged to work for the poor and protect Pakistan against “terrorists.”

Benazir Bhutto was assassinated in a gun and suicide bomb attack on December 27, 2007 while campaigning in the city of Rawalpindi. Ms. Bhutto was running as leader of the PPP in national elections. Shortly after her death, her husband, Asif Ali Zardari came to power as president.

Their son, Oxford-educated Bilawal Bhutto Zardari, is 24 years old and too young to run in a general election set for next year. Bilawal co-chairs the PPP with his father, President Zardari, who is unpopular and has been accused of corruption.

On Thursday, Bilawal Bhutto Zardari addressed thousands of supporters who gathered at the Bhutto family mausoleum in the Garhi Khuda Bakhsh village in the southern province of Sindh to mark the anniversary of the former prime minister's death.

“My honorable mother Benazir Bhutto was killed publicly, my thousands of workers have been murdered, but we did not abandon Pakistan and would not abandon Pakistan. I ask my Baluch brothers don't leave my, Benazir Bhutto's and your Pakistan in the hands of tyrants. This is your Pakistan, this is mine and your Pakistan.”

During his impassioned speech, Bhutto Zadari also targeted the judiciary — demanding why it has taken so long for his mother's killers to be brought to justice. No one has been charged with the murder.

A United Nations panel issued a report in April of last year accusing the government of then-Pakistani President Pervez Musharraf of failing to provide adequate security for Ms. Bhutto.