HARARE, Zimbabwe — The Zimbabwean police defied a high court ruling issued at midnight on Sunday ordering the release of a renowned human rights lawyer, Beatrice Mtetwa, and continued to hold her on charges of obstructing justice, a rights group said Monday.

“They have defied that court order, and did not implement what they were told to do,” said Kumbirai Mafunda, spokesman for Zimbabwe Lawyers for Human Rights, an organization trying to win Ms. Mtetwa’s freedom.

At a news conference in Harare, Zimbabwe Lawyers for Human Rights harshly criticized the police for continuing to detain Ms. Mtetwa despite the court order. “Human rights lawyers will not be intimidated, will not bow,” said Precious Chakasikwa, a human rights lawyer and vice chairwoman of the organization. "For every Beatrice Mtetwa that these state agents and institutions put behind bars and attempt to embarrass, humiliate and punish without lawful cause, there are 10 other human rights lawyers waiting to take up the mantle."

Security officials arrested Ms. Mtetwa and three senior officials of the Movement for Democratic Change, Zimbabwe’s main opposition political party on Sunday, one day after a largely peaceful referendum on a draft constitution.