A Chinese television station has apologized after showing a map on a talent show that did not include self-ruled Taiwan as being part of China, one of Beijing’s most sensitive political issues.

China has never renounced the use of force to bring democratic Taiwan, which it considers an inalienable part of China, under its control. Defeated Nationalist forces fled to Taiwan at the end of a civil war in 1949.

All maps published in China have to show Taiwan has being one of the country’s provinces.

But in a talent show for foreigners learning Chinese on Hunan Television on Sunday, a map shown in the background colored in only the mainland of China in red and left Taiwan white, according to a screengrab published on the official People’s Daily’s website.

In a statement on its official microblog late on Tuesday, state-run Hunan Television said it was sorry, blaming an outside contractor for the error and a failure of its own internal controls to spot the problem before the broadcast.

“We feel a deep sense of dereliction of duty at the ‘problem map’ incident and feel deeply pained,” it said.

All of the station’s employees are resolute in their belief that Taiwan is a part of China and oppose any form of separatism for Taiwan, it added.

Those responsible for the mistake have been punished, the station said without giving details, and received “severe criticism.”

Relations between China and Taiwan have worsened since the election of Tsai Ing-wen from the pro-independence Democratic Progressive Party as Taiwan president in January.

While Tsai has pledged to maintain peace with China, Beijing suspects she wants to push for the island’s formal independence.