Chinese police shot dead another Tibetan protester in the restive Sichuan province, rights groups said Friday, bringing to at least three the number killed in deadly clashes this week.

Urgen, a 20-year-old Tibetan, died Thursday in Sichuan's Rangtang county when police fired into a crowd trying to stop them from detaining another man, the US-based International Campaign for Tibet (ICT) and India-based TCHRD said.

It was the third reported deadly clash this week in western Sichuan -- which has big populations of ethnic Tibetans, many of whom complain of repression -- in the worst unrest in Tibetan-inhabited regions in years.

Security forces also fired into two separate crowds of protesters in Luhuo and Seda towns on Monday and Tuesday -- also in Sichuan, a province in China's southwest that borders Tibet -- killing at least two.

A Rangtang government official surnamed Wu told AFP Friday that there had been no protest.

"It is not convenient to talk about this. There is no need to contact others at this moment. Nobody will tell you anything," he said.

Calls to at least 16 places in Rangtang including restaurants and hotels were either met with no comments or respondents said they had no knowledge of the matter.

The information is difficult to verify independently as the area appears completely sealed off. AFP reporters who tried to access western Sichuan this week were turned back by police on several occasions.

But according to ICT and TCHRD, which have sources with contacts in the area, the incident in Rangtang was triggered by a youth named Tarpa, who posted a leaflet stating Tibet must be free and the Dalai Lama must return.

He printed his name and photo on the leaflet and said authorities could arrest him if they wanted, ICT said.

Later that day, security forces came to detain him at home, and as they were taking him away, people tried to stop them. Police then shot into the crowd, killing Urgen and wounding several others, the group said.

The unrest comes at a time of rising tensions in Tibetan-inhabited areas, where at least 16 people have set themselves ablaze in less than a year -- including four this month alone -- prompting an increase in security.

Advocacy groups say the unrest stems from growing grievance among Tibetans on issues such as religious repression, a lack of freedom, and a feeling that their culture is being eroded by an influx of majority Han Chinese.

But Beijing insists that Tibetans enjoy freedom of religious belief and says their lives have been made better by huge ongoing investment into Tibetan-inhabited areas.

It blames the Dalai Lama -- Tibet's spiritual leader who fled China for India in 1959 after a failed uprising against Chinese rule -- for fomenting the unrest and trying to split Tibet from the rest of China, a claim he denies.

News of the latest bout of unrest comes after the New York-based Human Rights Watch warned protests in Tibetan-inhabited areas were gathering pace, with at least seven occurring in January -- not including the Rangtang clash.

A researcher for ICT based in India's Dharamsala -- where Tibet's exiled government is based -- also said at least 136 Tibetans had been detained this month or had disappeared in Sichuan.

"The police offer no documents to families to tell them about where their family members are," Zorgyi told AFP.

On top of this, an additional 30 Tibetans went missing in the last few days after Chinese authorities caught them protesting in two towns in Banma county, he said.