China's stifling lockdown of this Tibetan town has not only been about patrolling its sleepy streets, but also policing the minds of a community at the center of self-immolation protests against Chinese rule.

Soldiers with helmets, rifles, sticks and shields march in rows along this monastery town's main road against a backdrop of snow-speckled mountains, while police stare at passing cars, scanning license plates and faces of passengers for unwelcome visitors. In school dormitory rooms in the county, there are random checks for books that go against the ruling Communist Party establishment _ and the constant questions about political leanings.

"They'll ask you questions and if you answer with your true feelings, they will be very unhappy. If you keep quiet, they will also be unhappy," said a Tibetan who teaches at a school in Aba county and who spoke on condition of anonymity for fear of government reprisals.

"They want you to say that the party is good and their policies are good," he added.

Teachers also are banned from making any mention _ positive or negative _ of the Tibetan spiritual leader, the Dalai Lama, the teacher said during an interview in the neighboring county of Hongyuan.

Earlier this week, an Associated Press reporter managed to get through several checkpoints along the road leading to Aba, for a rare glimpse of a town that has been under lockdown for more than three years, as well as an apparent uptick in security this week ahead of sensitive anniversaries.

The Aba township government referred telephoned questions about the heavy police presence to Aba prefecture, where government and Communist Party offices denied that security was high.

The town sits among high-altitude valleys grazed by yaks on the Tibetan plateau in southwestern Sichuan province. The town's Kirti Monastery, a large compound with an enormous white stupa, occupies a position in Tibetan society like that of a major university. Its monks have been at the forefront of unrest since Tibetan communities across western China rose up in a rebellion in 2008 that was quashed by a massive and continuing show of force. Many of the nearly two dozen Tibetans who set themselves on fire in the past year were monks or former monks from Kirti.

During this week's trip, the county surrounding Aba was cordoned off with roadblocks, usually manned by paramilitary police in green uniforms. On the way into town, a large signboard declared in Chinese, with no translation in the local Tibetan language: "A peaceful Aba is built by all, a peaceful Aba is shared by all."

Authorities had used traffic cones and barricades to narrow the town's main two-lane thoroughfare to one lane. Military trucks with green canvas covers and police vehicles were parked in rows in front of shops and restaurants. An armored paramilitary police van followed a group of marching soldiers on patrol.

Police stood close by as Tibetans huddled with crimson-robed monks over games, repaired cars or sawed wood. Multicolored prayer flags strung up on rooftops or tied to lampposts fluttered in the wind.

Plainclothes security men _ easily identifiable by their close-cropped hair, dark clothing and sunglasses _ sat on the sidewalk, newspapers in hand.

Barricades and a police minivan were perched at the junction to the narrow lane leading to the monastery. The first thing visible down the lane was a large white-and-blue police station, a Chinese flag atop it.

Internet and cell phone text messaging services in the area have been cut. Only telephone calls are allowed, and many believe that most calls are tapped. Describing a code he uses to ask friends in Aba about trouble with authorities, the teacher said: "Sometimes I ask them, 'Is the wind over at your end strong?' If they say it's strong, then there is a problem."

The authorities have dragooned Tibetans working in the governments of neighboring counties to serve as surveillance staff in Aba _ putting them in the awkward position of policing their ethnic brethren, said another Tibetan teacher, from Hongyuan, who stayed for three days in Aba last week.

The Tibetans have been deployed with red armbands at shop and hotel entrances, said the teacher, who also spoke on condition of anonymity.

"When ordered to, they don't dare to say 'I won't go,'" he said. "Once they get there, the people in Aba look at them accusingly, as if to say: 'You're a Tibetan and you're also coming here to treat us this way?'"

By nightfall, the street turns quiet and most security forces retire to hotels, while four or five military trucks patrol until morning, the teacher said.

"The locals are definitely feeling very heavy-hearted, very frustrated, all day. The soldiers are everywhere," said the teacher. "At every moment, people wonder what will happen to the person next to them, what the soldiers will do to them."

Security appeared to be tightening ahead of March, a month of sensitive anniversaries including that of the deadly anti-government riot among Tibetans in Lhasa in 2008, when frustration about Beijing's constant vilification of the exiled Dalai Lama boiled over. The period also marks the anniversary of the Dalai Lama's flight from the region in 1959 after an abortive uprising.

While the Chinese government has sought to win over the region by boosting economic growth, Tibetans worry about the gradual erosion of their culture and religion amid an influx of majority Han Chinese.

"In the people's hearts, what they probably can't stand the most is that the authorities scold our living Buddha, the Dalai Lama. We cannot stand it when they scold him," the teacher said. "He's the person we are most loyal to."

Dozens of security vehicles poured into the Aba area throughout the first few days of the week, lights flashing. They drove past a school where a red-painted slogan on a wall reminded students: "Without the Communist Party, Tibetan areas would not be where they are today."

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