HONG KONG—China's national government tolerates an extensive network of secret jails in Beijing operated by provincial and municipal governments to prevent citizens from complaining to national officials, according to a report released here Thursday by Human Rights Watch.

The report was based on interviews with 38 former detainees who had gone to Beijing to complain about what they described as corruption or other abuses of power at lower levels of government. It said that guards at the “;black jails”; beat, sexually abused, intimidated and robbed men, women and teenagers.

Provincial and municipal officials in China are subject to a national civil service system that penalizes them based on the number of complaints received in Beijing about their management. Thus, local and provincial officials have a strong incentive to prevent petitioners from reaching the central government.

Sophie Richardson, the advocacy director for Asia at Human Rights Watch, said that abuses were widespread in China's prison system, which has some judicial supervision, but that they were worse in unofficial jails.

“;We're talking about a country with torture in formal detention centers, and the black jails are 10 floors down”; in terms of the treatment of detainees, she said.

Jeffrey Bader, the National Security Council director for East Asian affairs, said Monday in a conference call with reporters that President Barack Obama planned to raise human rights issues with President Hu Jintao when they meet next week in Beijing. While Bader did not mention the unofficial jails, he did say that Obama would discuss “;rule of law,”; a phrase that would cover a range of extrajudicial practices.

The jails have been the subject of news reports inside and outside China, but the new report offers many details of abuses. Central government officials continue to deny the jails exist.

“;There are no black jails in China,”; Qin Gang, a Foreign Ministry spokesman, said at a regular news conference in Beijing on Thursday. “;If citizens have complaints and suggestions about government work, they can convey them to the relevant authorities through legitimate and normal channels.”;

China has taken steps in recent months to safeguard the legal rights of those who run afoul of the authorities. New regulations drafted by the Ministry of Public Security and released on Monday by the State Council, or cabinet, ban forced labor at government-authorized detention centers, where people accused of crimes are held before trial. The new rules also bar officials at detention centers from charging detainees for expenses like food.

But Nicholas Bequelin, a Hong Kong researcher for Human Rights Watch, said that the new rules did nothing to help detainees at unofficial jails.

The unofficial jails have captured attention in recent months.

According to Chinese news media, a guard at an unofficial jail in an inexpensive guesthouse pleaded guilty on Nov. 4 to raping a 20-year-old woman from Anhui province who had come to Beijing to complain about harassment at her university. Nearly a dozen people reportedly witnessed the rape, and about 50 detainees, including the woman, managed to escape jail when the guard fled after the assault.

The court dismissed charges against the guesthouse and two provincial liaison officials, according to the official China Daily newspaper.