The US ambassador to China is making a rare visit to Tibet and has urged Chinese authorities to open the area up to tourists and diplomats, a US official said Thursday.

Gary Locke was visiting the tightly-controlled region with his family and several embassy officials from Tuesday until Friday this week, acting deputy State Department spokesman Patrick Ventrell said.

It was the first time since September 2010 that Beijing has granted a US ambassador access to Tibet.

"In his official meetings, Ambassador Locke discussed the importance of opening up access to Tibet for diplomats, foreign journalists and foreign tourists," Ventrell added.

"He also emphasized the importance of preserving the Tibetan people's cultural heritage, including its unique linguistic, religious and cultural traditions."

The visit came amid the backdrop of a wave of self-immolations by Tibetans protesting continued Chinese rule of the territory.

The Washington-based Radio Free Asia (RFA) said that a Tibetan nun died earlier this month after setting fire to herself on June 11 near Nyitso monastery in Daofu country of southwest China's Sichuan province.

RFA said the nun was the 120th person to set themselves alight since February 2009 in a wave of protests by Tibetans against what they view as Chinese oppression. Many of them have died.

The United States remained "concerned" by "the deteriorating human rights situation in Tibetan areas that has played a role in tragic self-immolations," Ventrell said.

It continued to urge Beijing to hold a "substantive dialogue with the Dalai Lama or his representatives without preconditions as the best means to address Tibetan concerns and the current unrest."