German Foreign Minister Heiko Maas on Monday called for more transparency from China regarding its treatment of Uighur Muslims, an ethnic minority in the far-western province of Xinjiang.

"Ultimately, it will firstly be about creating transparency to finally judge what's happening there," Maas said in Beijing after a meeting with Chinese Vice Premier Liu He.

Reports from journalists and human rights advocacy groups indicate that up to 1 million Uighurs from Xinjiang have been interned in camps in the past year, where they are taught Communist propaganda and forced to renounce their culture and religion.

Maas said all sides had an interest in transparency, but added that the existence of re-education camps would be unacceptable.

Ahead of Maas' visit, the Chinese embassy in Berlin accused Germany's parliament and government of interference after the question of China's treatment of the Uighurs was raised during a debate.

The debate was "blatant interference in internal affairs and a gross violation of China's sovereignty," the embassy said.