Early Kate Saunders of International Campaign for Tibet tweeted:

@katesictibet A young Tibetan monk set himself on fire at Kirti in Tibet; protests that followed were violently suppressed, news just emerging

Now Phayul is reporting the story with more details:

A Tibetan monk of Kirti monastery in Amdo Ngaba is reportedly dead after he set himself ablaze at a market near his monastery, according to a reliable source with contacts in the region.

The source said that Phuntsok, 21, of Kirti monastery carried out protest at the busy market of Ngaba around 4PM (Beijing Time) before immolating himself. It is not yet known what slogans he chanted during the brief protest that was, according to the source, aimed to mark the 3rd anniversary of bloody crackdown on Tibetan protesters in Ngaba on March 16, 2008.

Chinese police immediately arrived at the scene, doused the fire, and beat Phuntsok, said the source. As the police were trying to take him away in a waiting police van scores of Tibetans rushed to the scene and protected Phuntsok. The crowd later grew in numbers, and took Phuntsok to his monastery making sure the Chinese police did not take him away. According to unconfirmed information from Ngaba, Phuntsok has succumbed to his burns, and that his body is lying in a chapel of the monastery.

Hundreds of angry Tibetans immediately gathered at the main market and carried out protests against the Chinese government. They walked almost a mile from the main market chanting anti-government slogans before being dispersed by Chinese security forces. Troops have been brought in from neighboring areas to quell the protests. Hundreds of Tibetans were arrested, and several others sustained injuries from electric baton and iron rods used by Chinese soldiers on the protesters.

Reuters has more.