ABA, China -- The monk reached into the folds of his red robe, pulled out a small notebook, and gently slipped from its pages a tiny photograph.

The man in the creased picture was a relative. He used to be a fellow monk at the monastery perched in snow-wrapped mountains outside the town of Aba. Then a Chinese security officer killed him, the monk said.

It is a sorrow that cannot be spoken of in public. A local government 'working team' visits the monastery often, looking for signs of discontent, according to monks there. Sometimes, they said, when returning to their living quarters from chanting or studying, the monks find a door busted in and possessions scattered after a search.

The monk showed the snapshot as a way of explaining why ethnic Tibetans, mostly current or former Buddhist clergy, are setting themselves on fire in Aba and surrounding regions in an unprecedented show of protest against Chinese rule. Since March 2011, between 20 and 24 have committed self-immolations, according to rights groups. Of those, at least 13 are said to have died.

'China in our eyes is not fair or peaceful,' said the monk, a man in his early 40s who, like every ethnic Tibetan interviewed for this story, did so on the condition that he not be named and that certain details be withheld, for fear of getting dragged off by police. 'We are suffering a lot in our hearts, and when we can no longer bear it we burn ourselves to death.'

The Chinese government and its media have confirmed some of the self-immolations and denied others. But the government also goes to extensive lengths to prevent outsiders from visiting this area. Police routinely block roads, search vehicles and turn back foreigners, especially journalists.

A McClatchy Newspapers reporter last week became the first from an American news organization to make it to Aba since the chain of self-immolations began. To do so, he hid on the rear floor of a vehicle under two backpacks and a sleeping bag as it passed through multiple checkpoints.

Beijing has long blamed unrest in ethnic Tibetan areas on conspiracies hatched by the Dalai Lama, the Tibetan spiritual leader who fled to India after a failed uprising against Chinese rule in 1959.

But conversations with ethnic Tibetans here and elsewhere in Sichuan province, where almost all of the self-immolations have occurred, suggest that China's authoritarian policies designed to tamp down disorder are fueling the troubles.

As the nation's vice president and presumptive next leader, Xi Jinping, tours the United States this week amid talk of greater understanding, his government at home continues to flood a wide swath of ethnic Tibetan lands with armed troops.

At the entrance to Aba last week, at least seven police officers manned a checkpoint. When an SUV approached with a Han Chinese man in the front seat, it was allowed to pass without a question -- as the McClatchy Newspapers reporter lay in the back.

Ethnic Tibetans face tougher scrutiny. One Tibetan from a nearby village described the interior of his taxi being almost ripped apart during a search at the entry of Aba, which is known in Tibetan as Ngaba.

About the same time the reporter entered Aba on Saturday, an 18-year-old woman in a nunnery near the town's outskirts was setting herself on fire. The ethnic Tibetan nun, Tenzin Choedon, reportedly called out slogans against the government as the flames took her life.

Sections of the town famous for its Tibetan Buddhist monasteries have come to resemble an armed camp. A few blocks from the entrance, paramilitary police stood behind riot gates with shotguns and assault rifles. Three large troop-carrier trucks sat on the side of the road, flanked by more men with guns. Up ahead, traffic wound through further riot gates and troop positions not unlike those used in counterinsurgency efforts.

The security was so dense that it was impossible to speak with clergy or, indeed, anyone in Aba because of the risk of bringing danger to those interviewed. The Internet had been shut off and efforts to send text messages from Aba failed repeatedly.

Police roadblocks and patrols in the region begin just outside the city of Chengdu, hundreds of miles away. Even in that sprawling metropolis, Chengdu's main Tibetan quarter is stacked with police who stand guard outside restaurants and shops that sell incense and religious paraphernalia.

An attempt in November to reach Aba ended with a McClatchy reporter being held and questioned by Chinese police for two hours before he was released and told to return to Beijing.