Following the self-immolation of more than 20 Tibetans in the last year, the Chinese authorities say they are preparing for "a war against secessionist sabotage".
At least 21 Tibetans have set themselves on fire in a spate of suicides and attempted suicides that began early last year.
Most of the self-immolations were carried out by Buddhist monks and nuns, some of them believed to be as young as 17.
Tibetan exile groups say several of those who set themselves alight chanted slogans calling for greater religious freedom as they burned.
Many Tibetans in China complain of heavy-handed government interference in their religious practices, including forced "political education" sessions in monasteries.
The Chinese authorities have described the self-immolations as "terrorism in disguise" and say they are "obviously incited and masterminded by someone behind the scenes" - a thinly-veiled reference to the exiled Tibetan spiritual leader, the Dalai Lama.
The Dalai Lama has condemned the self-immolations but says that Tibetans are being driven to acts of desperation.
The most recent reported self-immolation was an 18-year-old man named Dorjee.
On Sunday, a widowed mother of four is thought to have died after setting herself on fire in Aba, the small, predominantly Tibetan town in China's Sichuan Province where most of the self-immolations have occurred.
Police have detained several foreign journalists attempting to enter the area, but a Sky News crew managed to slip through police checkpoints and film a town under a virtual lock down.
Dominated by Kirti Monastery, a sprawling complex that houses several hundred Buddhist monks, Aba has now been swamped by Chinese paramilitary police.
Ranks of men in anti-riot gear crouch behind the steel barricades that line the town's main street, while camouflaged troops use a field less than 200 yards from the monastery's golden stupa to practice martial arts drills.
Though no violent protests have been reported in Aba, unrest in nearby Ganzi has left at least two people dead.
China's state media says that Tibetan rioters, including monks, stormed police stations and threw Molotov cocktails. Tibetan exile groups accuse Chinese police of opening fire on peaceful demonstrators.
There are also unconfirmed reports that a Tibetan man died this week when he detonated a bomb in a government building in the town of Dege.
After leaving Aba the Sky News crew was detained by police who forcibly searched bags and deleted files from an audio recording device.
They temporarily confiscated a computer and camera, threatened to revoke Chinese visas and then followed the car for 300 kilometres (187 miles).