Federal Capital Territory (FCT) police spokeswoman Altine Daniel confirmed the ban in a text message to AFP, saying the decision was taken "because of security reasons".
Protest organisers questioned the legitimacy of the move and eyed a possible political motive, but police chief Joseph Mbu said the ban was imposed because of the threat of infiltration from "dangerous elements".
"There is no basis for and no power of FCT Commissioner of Police to ban peaceful assembly of any group of persons in... The city," said protest leader Oby Ezekwesili on Twitter.
'Bring Back Our Girls' spokesman Rotimi Olawale said that the protesters were "unperturbed" and would meet again in the capital on tomorrow.
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"We have been peaceful in our protest. We don't obstruct traffic or constitute ourselves to a public menace," he added.
Families and supporters of the missing girls were critical of Nigerian President Goodluck Jonathan's response to the abduction, accusing him of being slow to react and indifferent to their plight.
In the weeks after the April 14 abduction, Nigeria has been forced to accept foreign help, including from the United States, to try to find the girls.