China has sentenced a popular Tibetan singer to four years in prison for calling on Tibetans to unify and speak their language, reports said, highlighting tight cultural controls in the region.

Kalsang Yarphel, 39, was convicted by a court in the southwestern province of Sichuan after taking part in concerts encouraging people to speak and learn Tibetan, India-based news website Phayul.com reported on Sunday.

"Authorities accuse him of singing songs that have political overtones," Phayul.com reported, adding that Yarphel's music arranger was also sentenced to two years in jail.

It was not clear what crime the singer - who blends traditional Tibetan instrumentation with pop influences - was convicted of last Thursday, AFP news agency reported.

US-based broadcaster Radio Free Asia (RFA) cited a local source as saying: "He was indicted for organising Tibetan concerts and singing songs...carrying political themes."

Yarphel's songs included "We Should Learn Tibetan" and "We Should Unite", RFA reported, adding that he was detained last year. The concerts were in 2012, the reports said.

'Build courage'

The singer's call for Tibetans to "build courage" to think about Tibet's "future path" was deemed subversive by Chinese authorities, RFA added.

Wary of challenges to its rule, Beijing tightly controls cultural and religious practices in Tibet, and many Tibetans complain of economic discrimination.

Controls have tightened since a wave of deadly riots in Tibet's capital Lhasa in 2008.

Beijing says it has brought economic development to poverty-stricken Tibetan areas, and that it grants broad religious freedoms.

At least 130 Tibetans have set themselves on fire since 2009 in protest at Beijing's rule, with most of them dying.

China says that the exiled Tibetan spiritual leader the Dalai Lama has encouraged the immolations, and has warned foreign governments against meeting with him.

Beijing heavily restricts journalists in Tibetan areas, making reports hard to confirm. Authorities in Sichuan province could not be reached for comment.

Source: Agencies