China has confirmed that a Tibetan was shot dead by security forces in Sichuan province, in the second day of unrest this week.
Local officials said a mob attacked a police station in Seda county on Tuesday, Xinhua news agency reported.
Tibetan activist groups said security forces fired on people protesting against religious repression.
On Monday, at least two other protesters were killed in neighbouring Draggo county.
There are large communities of ethnic Tibetans in several parts of Sichuan province, which borders Tibet.
Accounts of violence in the area differ and are difficult to verify. Foreign media, including the BBC, are rarely allowed access there.
Xinhua news agency said that police used force in Seda "after efforts involving persuasion and non-lethal weapon defence failed to disperse the mob". Its report said one "rioter" was killed.
Police said that the mob attacked the police station "with gasoline bottles, knives and stones" and "opened fire at us".
Xinhua also quoted experts from the Sichuan Tibetan Research Institute as saying that the two "attacks" in Sichuan province were "premeditated and organised violence".
But Tibet campaign groups dispute this version of events and say at least two people were killed in Seda. UK-based Free Tibet says that the town is now under curfew, citing local residents.
Free Tibet director Stephanie Brigden said in a statement on Wednesday that China was "responding with lethal force" to Tibetans' "calls for freedom".
On Monday, it was reported that at least two people were killed in another clash in Sichuan province.
Chinese state media said a mob armed with knives ''stormed and smashed some stores along a main street and a police station'', and also destroyed four vehicles in Draggo county.
Activists say Chinese security forces opened fire on peaceful demonstrators.
Free Tibet reported two dead, while the Tibetan parliament-in-exile in India and the US-based rights group International Campaign for Tibet put the death toll at three. Xinhua said one person died.
A monk from the monastery in Draggo told the Associated Press news agency in a telephone interview on Tuesday that 33 people were being treated for injuries at the compound.
The US state department has expressed serious concern about the reports, urging the Chinese government "to engage in a constructive dialogue with the Dalai Lama or his representatives as a means to address Tibetan concerns".
But Chinese foreign ministry spokesman Hong Lei said on Tuesday that "overseas secessionist groups" were trying to discredit the government.
In recent months, however, there have been several protests and incidents in ethnic Tibetan parts of Sichuan province.
Since March 2011, 16 ethnic Tibetans have set themselves on fire in what are described as protests at perceived cultural and religious repression under Chinese rule. Several of them are known to have died.
The authorities in Beijing have moved to suppress religious activism since riots in Tibet four years ago killed 19 people.
China's government has described the self-immolators as terrorists and has accused the Dalai Lama of encouraging their actions in order to put pressure on the authorities to make political concessions.