Sharif, who returned recently to Pakistan from exile in Saudi Arabia as did Bhutto from Dubai, called her assassination a tragedy for the entire country.
He visited the hospital where Bhutto was taken after she was fatally wounded.
"I can't tell you what the feelings of the people of Pakistan are today," Sharif told the BBC.
Subsequently Sharif announced his Pakistan Muslim League-N party would boycott the Jan. 8 parliamentary elections, the BBC reported.
Sharif also called on President Pervez Musharraf, who removed him from power in 1999 in a bloodless coup, to resign, saying free and fair elections are not possible under Musharraf's rule.
Earlier this month, the Pakistan election commission refused to review a ban on Sharif running in the elections. The original ban issued by a returning officer last month was reportedly based on Sharif's past criminal convictions. Sharif has said the charges were trumped up.
Musharraf ended his 6-week-old emergency rule early this month and restored the constitution. He, however, refused to reinstate the judges he dismissed during the emergency. Sharif had been campaigning for their reinstatement.