A Tibetan author jailed by China for writing a book about the Himalayan region has been released after a decade in prison, a US-based rights group said.

Dolma Kyab, 39, was freed last week after being convicted a decade ago of "endangering state security," the International Campaign for Tibet said late Tuesday.

Tibet is tightly controlled by China's ruling Communist party, which is intolerant of public opposition to its policies, and often jails dissidents.

Kyab's trial happened in secret in Tibet's capital Lhasa and only came to light after a letter he wrote while incarcerated was smuggled out of prison months after his 2005 sentencing.

According to a copy of the letter seen by the rights group at the time, Kyab said he was imprisoned because the ideas he expressed in his unpublished book "The Restless Himalayas".

He added that authorities believed his writing was "connected to Tibetan independence".

In his book, Kyab wrote about conceptions of Tibetan identity as well as Tibetan hopes for exiled spiritual leader the Dalai Lama to return to his homeland, the ICT said.

In it he told his "Tibetan brothers and sisters: We live in a time of national devastation. We have weathered countless years of darkness, countless dark nights."

He also wrote about the "political burden" suffered by Tibetans because China's Han majority "impose their way of thinking onto Tibetans", thus "destroying the concept the Tibetans have of themselves".

China, which has ruled Tibet since the 1950s, has been accused of trying to eradicate its Buddhist-based culture through political and religious repression and large-scale immigration by Han Chinese.

Beijing says that Tibetans enjoy extensive freedoms and that it has brought economic growth to the region.

Tibetan spiritual leader the Dalai Lama fled Tibet after an abortive uprising in 1959 and established a government-in-exile in Dharamsala in India.

After his release from the Qushui Prison in Lhasa, Kyab was taken back to his home town, where family and friends draped him with white blessing scarves, ICT reported.

US urges release of Chinese rights lawyer
Washington (AFP) Oct 14, 2015 - Washington on Wednesday renewed its call for China to release a Christian rights activist detained just before he was to meet a US envoy researching religious freedom.

Secretary of State John Kerry and the envoy, Ambassador David Saperstein, urged Beijing to free lawyer Zhang Kai, as they released a report on religious persecution.

"I urge the release of men and women detained or imprisoned anywhere in the world for the peaceful expression and practice of their religious beliefs," Kerry told reporters.

"This includes Mr Zhang Kai, a Chinese Christian human rights lawyer who was detained in late August just prior to a scheduled meeting with Ambassador Saperstein, and whose present whereabouts are unknown."

As part of the preparation for the State Department's annual report into the state of religious freedom around the world, Saperstein visited China August 20-28 to meet officials and activists.

Launching his report, Saperstein said that in areas where the Chinese government's "hand is lighter" there are flourishing religious communities, but that in some regions a harsh crackdown is under way.

That included Zhang, described by Saperstein as "peaceful, respected."

China's ruling Communist Party keeps tight control over religion for fear it could challenge its grip on power, requiring believers to worship in places approved by the state and under government supervision.

And since President Xi Jinping came to power in 2013, the government has taken a harder line towards civil and religious society.

More than 200 lawyers and activists, including Zhang, were questioned or detained in July as part of a sweeping nationwide crackdown.

In Wenzhou, in the eastern province of Zhejiang, authorities have stepped up a long-running campaign to remove crosses and several churches have been destroyed.

"We were denied permission to actually travel there, but we were allowed to go to the capital of that province," Saperstein said.

The US envoy told reporters in Washington that three human rights lawyers, four pastors and three or four other activists were detained before he could meet them.

Most have been released, but not Zhang, whom the US official described as "one of the most respected human rights lawyers in China, someone who has argued over and over again that they have to work within the legal system of China in order to win these battles and has proved very skilled at doing that, representing a range of religious groups."