Nigerian police have banned public protests in the capital, Abuja, for the release of more than 200 schoolgirls seized by Islamist militants in April.
Abuja police commissioner Joseph Mbu said the rallies were "now posing a serious security threat".
Nigeria has seen almost daily rallies calling for the government to take firmer action to rescue the girls.
Boko Haram militants snatched the girls from the remote Chibok village near the Cameroon border on 14 April.
The ban comes after scuffles broke out last week between the demonstrators organised under the #BringBackOurGirls and a new government-sponsored group called #ReleaseOurGirls.
In a statement, Mr Mbu said that public protests had "degenerated" and were now a security threat.
He was also quoted by the state-run Agency of Nigeria as saying that "dangerous elements" could join the demonstrations.
But one of those involved in the #BringBackOurGirls demonstration, Jibrin Ibrahim - director of the Abuja-based Centre for Democracy and Development, said the protesters planned to challenge the ban in court.
"We are sure that the courts will affirm our right to exercise constitutional rights and that therefore we'll be able to continue with our protest," he told the BBC's Newsday programme.
He said the only threat came from the #ReleaseOurGirls group.
"The government funded a group to come and disrupt our peaceful sit-in and attack us and he is now using that fact to say there is a threat," Mr Ibrahim said.
It was strange the government should feel that protesters could not call on it to provide nationwide security - its "constitutional responsibility", he said.
Nigeria's government has been facing growing pressure both at home and abroad to do more to tackle the group and bring about the girls' release.
A deal for the release of some of the abducted schoolgirls in Nigeria was close to being secured when the Nigerian government called it off late last month, the BBC has learned.
Some of the girls were set to be freed in exchange for imprisoned Islamist militants, reports the BBC's Will Ross.
Thousands of people have died since Boko Haram began a violent campaign against the Nigerian government in 2009 and in the subsequent security crackdown.
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