BEIJING, China (CNN) -- Chinese authorities should abolish secret jails used to unlawfully detain citizens who travel to the capital and other major cities to file complaints, Human Rights Watch says.
For the past six years, citizens have been held without communication in so-called black jails, often located in state-owned hotels, nursing homes and psychiatric hospitals, according to a new report from the human rights group.
Most of the detainees are from rural areas and travel to major cities to submit grievances at petitions and appeals offices, which address cases without going to court, Human Rights Watch said.
Government officials and security forces often beat, abuse, threaten and intimidate the detainees to ensure that their complaints do not draw attention, according to the report.
"The existence of black jails in the heart of Beijing makes a mockery of the Chinese government's rhetoric on improving human rights and respecting the rule of law," said Sophie Richardson, Asia advocacy director of Human Rights Watch.
"The government should move swiftly to close these facilities, investigate those running them and provide assistance to those abused in them."
China has repeatedly denied the existence of secret jails, and the ministry of foreign affairs reiterated that stance Thursday.
"I'm not sure what evidence the report of Human Rights Watch is based on," the office said in a statement. "However, I can tell you that there is no such black jails in China."
The judicial system will deal with relevant cases, the ministry said.
"If there is any suggestion or complaint from Chinese people toward our government, they can appeal to relevant departments through normal and legal channels, and their legitimate rights will be protected."
But the rights group said the jails are becoming more popular because officials are penalized if too many grievances come from their jurisdictions. Areas with fewer complaints are rewarded, it said.
In the report, titled, "An Alleyway in Hell," the group said it had interviewed 38 people who have been detained in the facilities.
The detainees include people under 18, which violates China's commitments to children's rights, Human Rights Watch said.
A 15-year-old told the group she was seized in Beijing while petitioning on behalf of her crippled father, who was subjected to beatings at his nursing home.
"To visit these kinds of abuses on citizens, who have already been failed repeatedly by the legal system, is the height of hypocrisy," Richardson said.
The New York-based organization urged the U.S. president to address human rights issues during his trip to Asia, which starts Thursday and will include a stop in China.
"President Barack Obama has spoken forcefully about the importance of defending human rights globally," said Kenneth Roth, executive director of Human Rights Watch. " ... The test now is whether he will do so in a country where the government remains profoundly hostile to these concepts."
CNN's Helena Hong contributed to this report.