BEIJING (Reuters) – China denounced the United States on Thursday for passing a new law on restive Tibet, saying it was “resolutely opposed” to the U.S. legislation on what China considers an internal affair, and it risked causing “serious harm” to their relations.

U.S. President Donald Trump on Wednesday signed into law the Reciprocal Access to Tibet Act.

The law seeks to promote access to Tibet for U.S. diplomats and other officials, journalists and other citizens by denying U.S. entry for Chinese officials deemed responsible for restricting access to Tibet.

Beijing sent troops into remote, mountainous Tibet in 1950 in what it officially terms a peaceful liberation and has ruled there with an iron fist ever since.

Chinese foreign ministry spokeswoman Hua Chunying told a daily briefing that the law “sent seriously wrong signals to Tibetan separatist elements”, as well as threatening to worsen bilateral ties strained by trade tension and other issues.

“If the United States implements this law, it will cause serious harm to China-U.S. relations and to the cooperation in important areas between the two countries,” Hua said.

The United States should be fully aware of the high sensitivity of the Tibet issue and should stop its interference, otherwise the United States would have to accept responsibility for the consequences, she added, without elaborating.

Rights groups say the situation for ethnic Tibetans inside what China calls the Tibet Autonomous Region remains extremely difficult. The U.N. High Commissioner for Human Rights said in June conditions were “fast deteriorating” in Tibet.

All foreigners need special permission to enter Tibet, which is generally granted to tourists, who are allowed to go on often tightly monitored tours, but very infrequently to foreign diplomats and journalists.

Hua said Tibet was open to foreign visitors, as shown by the 40,000 American visitors to the region since 2015.

At the same time, she said it was “absolutely necessary and understandable” that the government administered controls on the entry of foreigners given “local geographic and climate reasons”.

Tibetan rights groups have welcomed the U.S. legislation.

The International Campaign for Tibet said the “impactful and innovative” law marked a “new era of American support” and was a challenge to China’s policies in Tibet.

“The U.S. let Beijing know that its officials will face real consequences for discriminating against Americans and Tibetans and has blazed a path for other countries to follow,” the group’s president, Matteo Mecacci, said in a statement.

Next year marks the sensitive 60th anniversary of the flight into exile in India of the Dalai Lama, the highest figure in Tibetan Buddhism, after a failed uprising against Chinese rule.

China routinely denounces him as a dangerous separatist, although the Dalai Lama says he merely wants genuine autonomy for his homeland.