The United Nations barred a visitor from entering its headquarters last week because she was wearing a patch on her coat with the words "Black Lives Matter".
The world body insisted last night that the ban is in keeping with long-standing UN rules.
The phrase "Black Lives Matter" has become a rallying cry for demonstrators across the United States protesting grand jury decisions not to charge white police officers in the killings of unarmed black men in Ferguson, Missouri, and New York City.
A security officer told the woman who attempted to enter the United Nations in New York City last Friday that the patch on her coat would violate a ban on political protests inside the UN compound. The woman, who declined to be identified, was allowed to enter the building after removing it.
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"There is a long-standing organisational policy that does not permit visitors to come in wearing political messages, display banners or distribute leaflets outside of a planned event and with proper authorisation," a UN spokesman said at a news conference.
"In this case the security officer acted properly in accordance with regulation," he added.
UN Secretary-General Ban Ki-moon spoke out in support of the right of demonstrators to peacefully protest after a grand jury last month cleared a white police officer in the fatal August shooting of Michael Brown, an unarmed black teenager in Ferguson.
The United Nations headquarters are situated in New York City but the complex exists on international territory administered by the UN secretariat.Reuse content