Meanwhile, a US diplomat was allowed on Thursday to cross the barricades and heavy police cordon surrounding the house in Lahore where Bhutto had been confined.
Sherry Rehman, a Bhutto spokeswoman, said Bryan Hunt, the US consul-general in Lahore, was making merely a "courtesy call" on Bhutto.
John Negroponte, who last week cautioned against cutting aid to an "indispensable" ally, is due in Pakistan this week.
Another opposition figure contacted by Bhutto earlier in the week, Imran Khan, the former cricket captain, was moved to Lahore's biggest prison early on Thursday after being charged under anti-terror laws for protesting against emergency rule.
Kamal Hyder, Al Jazeera's correspondent in Islamabad, said on Thursday that two of Khan's sisters and at least thirty other women have been arrested while protesting in Lahore.
In a separate development, two boys were killed when gunfire erupted in the southern Pakistani city of Karachi during a protest by Bhutto's supporters.
The deaths were the first since Musharraf imposed the state of emergency.
Fayyaz Khan, a Karachi police official, said: "There was a demonstration against the house arrest of Benazir Bhutto. Somebody among the demonstrators opened fire and two boys aged around 11 or 12 were killed."
Khan said there had been gunfire for the past three days during rallies by the PPP in the neighbourhood of Lyari, a party stronghold.
Ijaz Durrani, a PPP spokesman, denied any of its supporters had opened fire and suggested the involvement of undercover police. He had earlier blamed a local drug mafia.
Durrani said: "Our protesters came under attack, maybe some policemen in civilian clothes could be involved in the firing. We are investigating but we suspect police involvement.
"We do not believe in gun culture. Our people were peaceful, they never indulge in such incidents."