An overnight bomb blast ripped through a government building in Tibet, causing damage but no injuries, London-based campaign group Save Tibet told AFP on Thursday, citing two sources.
"Several sources have confirmed a bomb blast but nothing is known about who carried it out or why," spokeswoman Kate Saunders told AFP by telephone.
"As it was carried out at 4:00 am, it is thought that no one was hurt," she added, saying the blast in Karma town in Chamdo prefecture was either on Wednesday or Thursday morning.
Tibetan news portal www.TibetExpress.net also reported the news, saying "Tibet's independence" had been daubed in red on the damaged walls of the office building and "Free Tibet" fliers had been found at the scene.
"No one is accused or arrested in this connection so far but the entire road access leading to and from Chamdo had been completely cut off including closure of Karma monastery," the source told the website.
The author of the report, journalist Tenzin Wanchuk, said he had received the information from a source in Karma county who said the explosion took place on Wednesday morning.
"We got this information from a person who called us from that area and said he had seen the bombing. The information is authentic but we cannot identify him," he said.