Saud Aziz, Rawalpindi's police chief, said: "If they try to flout the ban, the law would take its course."
Javed Akhlas, the mayor of Rawalpindi, said police would be out in force to prevent anyone reaching the park where Bhutto hoped to address supporters.
"We will ensure that they don't violate the ban on rallies, and if they do it, the government will take action according to the law," he said.
Bhutto, in her strongest comments since Musharraf imposed emergency rule, said the world must make Pakistan's military leader revoke his measures or tell him to quit.
"Musharraf has many enemies in his country and I believe with Bhutto as PM there would be more people supporting the goverment"
Howahr, Doha, Qatar
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"If he doesn't, then I believe that the international community must choose between the people of Pakistan and him," Bhutto said in an interview with British tv broadcaster Channel 4.
The former prime minister returned to Pakistan on Tuesday, but said that a meeting with Pervez Musharraf, Pakistan's president, was "not in her schedule during her stay in Islamabad".
Musharraf and Bhutto had been in contact for several months prior to her return, discussing a possible power-sharing deal.
The president granted her an amnesty on corruption charges in October to allow her to return home.
'Path of destruction'
Also on Wednesday, Imran Khan, the Pakistani cricketer-turned-politician, also called for protests against Musharraf in a video broadcast on the private Geo TV.
"If we don't resist, it will take Pakistan on the path of destruction," Khan said in the short video message.
The former cricketer withdrew from public appearances on Sunday, a day after police placed him under house arrest at his home in the eastern city of Lahore.
"Imran is safe. From an unknown place he is leading the movement," said Jawaid Iqbal, a retired admiral and a spokesman for Khan's Movement for Justice party.
Iqbal also said the situation in Pakistan "is worse than Iraq at the moment".
Hundreds of people, mostly lawyers and opposition politicians, have been detained in Pakistan since Musharraf imposed emergency rule on Saturday.
Lawyers scuffled with police during a third day of demonstrations on Wednesday, protesting against Musharraf's weekend declaration of a state of emergency.
A violent clash with Bhutto's supporters at the planned rally could dramatically escalate the political crisis in the country.
Chaudhry Shujaat Hussain, the president of the ruling Pakistan Muslim League and a member of Musharraf's inner circle, has told the local press that the emergency rule is likely to end in "two to three weeks".
"I'm sure it will end in two to three weeks as president Pervez Musharraf is aware of the consequences of long emergency rule," Hussain said in the Dawn's Wednesday edition.
Musharraf also dismissed Iftikhar Muhammad Chaudhry, the country's chief justice, from the Supreme Court.
Chaudhry on Tuesday urged supporters to "rise up", take to the streets and demand the restoration of the constitution and the lifting of the emergency measures.