Police in China shot dead two more protesters in Tibetan-inhabited areas as unrest spread, official media and an advocacy group said Wednesday, amid signs of a physical and virtual lockdown on the region.

China’s Sichuan province, which has big populations of ethnic Tibetans, many of whom complain of severe repression, has been rocked by violent clashes this week — some of the worst since huge protests against Chinese rule in 2008.

The US on Tuesday said it was “seriously concerned” by the situation, calling on Chinese security forces to “exercise restraint” and urging authorities to allow journalists and diplomats into flashpoint areas. There were indications on Wednesday that the authorities were restricting movement and communications in the region as unrest spread. Phone numbers that previously worked were suddenly unavailable and one local said his town had been closed off by authorities.

The situation has prompted Lobsang Sangay, head of the India-based Tibetan government-in-exile, to call on the international community “to not remain passive” and “to intervene to prevent further bloodshed”. The unrest comes at a time of increasing tensions in Tibetan-inhabited areas, where at least 16 people have set themselves ablaze in less than a year — including four this month alone — over a lack of religious freedom.

In the latest bout of violence, police opened fire on a protest in Seda county on Tuesday, killing two protesters and injuring scores of others, according to the exiled Tibetan government and advocacy group Free Tibet.