BEIJING -- A Chinese anti-discrimination civic group said Friday it is considering legal action over a police raid on the group's offices that was apparently prompted by its advocacy for five women's rights activists whose detentions have drawn international scrutiny.

Beijing Yirenping Center head Lu Jun said he is still seeking more information about Tuesday's pre-dawn raid on the group's offices in which officers carted off computers and financial documents. The group believes the seizures were illegal and wants to see whether it can file a lawsuit against the police, Lu said.

"This is definitely not over yet," Lu said by telephone from the U.S., where he is a visiting scholar at New York University's U.S.- Asia Law Institute.

The centre is currently under police lockdown, its advocacy on hold and its staff scattered to avoid being picked up by police. A security guard at the building confirmed the basic details of the raid, while a Beijing police spokesman said he had no information about it but would make inquiries.

Lu said he believed the raid was retaliation for the centre's campaign for the release of the five women's rights activists who were detained ahead of International Women's Day on March 8. They had planned to mark the occasion by distributing anti-sexual harassment materials to the public in three Chinese cities. Their detention has drawn strong criticism from European Union and the United States.

However, Lu said the police action was part of a sweeping crackdown against non-governmental organizations as a whole that has intensified over the past six months under the leadership of President and Communist Party leader Xi Jinping.

Many NGOs and rights activists -- regarded by the party as agents of foreign infiltration -- have been harassed, threatened and detained, while government leaders and state media have issued strident warnings about the penetration of liberal "Western values" into society and university classrooms.

By coincidence, Tuesday's raid coincided with the start of five days of inspections by the International Olympic Committee of Beijing's bid to hold the 2022 Winter Olympics.

Rights groups opposed to the bid have highlighted China's restrictions on free speech and assembly and allegations of gender discrimination, meeting with harsh denunciations from bid organizers.

China's Foreign Ministry has rejected growing international calls for the release of the five women, including from U.S. Ambassador to the UN Samantha Power, Britain's Foreign Office and the European Union. A ministry spokeswoman on Wednesday defended China's legal system and demanded such critics "stop interfering in China's judicial sovereignty in such a manner."

Wei Tingting, Li Tingting, Wang Man, Zheng Churan and Wu Rongrong have been held in a Beijing detention centre for almost three weeks, accused of creating a disturbance. If convicted, they could be sentenced to up to three years in prison. Five others detained at the same time have since been released.

Lawyers for the women say they are being held under harsh conditions, are subject to lengthy interrogations and have been denied access to legal counsel.

Beijing police say they have no information about the five.