Human Rights Watch on Wednesday condemned a Chinese "para-police" force nicknamed "X-Men" by the local media, accusing it of rampant brutality and illegal detentions for even minor offences.

The New York-based rights group issued a 76-page report documenting abuses by the Urban Management Law Enforcement agency, known as the "chengguan", and urged China to reform or even abolish the force.

"In numerous recent Chinese state media editorials, the chengguan have been... derided as law-breaking 'X-Men'," the group said in the report, entitled "Beat Him, Take Everything Away".

Sophie Richardson, China director at Human Rights Watch, said the agency's "abusive conduct turns the idea of rule of law on its head".

"The chengguan's ability to flout China's laws and inflict harm on members of the public is a recipe for greater public resentment and more violent confrontations," she said.

Founded in 1997, the force constitutes an urban administrative police unit made up of thousands of security officers in at least 656 Chinese cities, the Human Rights Watch report stated.

Its principal role is to enforce rules in non-criminal areas such as the environment, sanitation, traffic and urban beautification and it has the power to impose fines on violators.

However, it routinely goes much further, according to HRW, detaining or using excessive force against those suspected of violating administrative rules, even though it does not have the legal authority to do so.

"Chengguan forces have earned a reputation for brutality and impunity," said Richardson.

"They are now synonymous for many Chinese citizens with physical violence, illegal detention and theft."

The report documented 25 cases where the agency allegedly used physical violence, illegal detention, arbitrary fines and the illegal confiscation of goods and merchandise while carrying out its duties.

It said officers routinely crack down on illegal street vendors, but have also been used to evict tenants in government-backed land grabs -- one of China's most explosive social issues.

Local resentment over the agency's actions has also led to vocal and violent protests, according to the report.

The press office of China's State Council, or cabinet, refused to immediately comment on the report when contacted by AFP.

Human Rights Watch urged China to issue new and uniform laws on the behaviour of the agency's personnel, transfer its duties to the nation's police force, or abolish the agency altogether.