It read like a muckraking expose: A magazine revealed a system of secret detention centers in Beijing where Chinese citizens are forcibly held and sometimes beaten to prevent them from lodging formal complaints with the central government.

But the report appeared in the state-run magazine Liaowang (Outlook), which is written for the government elite and published by China's official Xinhua News Agency.

For some activist groups, the two state-sanctioned articles published Tuesday signal a possible willingness by the Communist leadership to openly acknowledge a problem it has long denied.

"They have categorically denied there are even black jails. This is the first time an official, high-level magazine acknowledges that they exist. This is fairly significant," said Wang Songlian, research coordinator with the China-based Chinese Human Rights Defenders.

Detailed reports about these illegal lockups, known as "black jails," are not new. They have been widely documented by human rights groups, academics and international media.

The victims are mostly petitioners: ordinary Chinese who travel to Beijing and other provincial capitals seeking a resolution to grievances _ including corruption, land grabs and abuse _ that local officials have ignored. They are grabbed off the street, often by those very local government officials or their agents, and held captive in run-down hotels, nursing homes and even psychiatric hospitals until they can be sent home. Often, police either ignore or actively cooperate with the "retrievers."

But the Chinese government has repeatedly insisted that the unofficial jails don't exist. Two weeks ago, Foreign Ministry spokesman Qin Gang flatly rejected a Human Rights Watch report on the detention centers.

On Wednesday, the Foreign Ministry and Public Security Ministry declined to comment on the articles and referred questions to the State Bureau for Letters and Visits, where a staffer hung up the phone.

The two articles, prominently displayed on the home page of Xinhua's Web site, come just a week after President Barack Obama's visit _ when he raised human rights concerns _ and two weeks after the Human Rights Watch report.

In China, where media organizations are very tightly controlled and content often censored or restricted, a lengthy piece on a taboo topic is unlikely to have been an accident, say longtime China watchers.