The Chinese national who oversaw rare metals was arrested in March, Japan’s Nikkei newspaper says.

Chinese authorities detained a local employee of a Japanese trading firm this year, The Nikkei newspaper has reported, amid a spate of raids on foreign companies and detentions of their staff in China.

The report, citing sources and released late on Sunday, did not identify the firm or the staff member, only saying the person was a Chinese national who oversaw rare metals at the company. The reason for the detention was unknown, the report said.

China’s Ministry of Foreign Affairs did not immediately respond to a request for comment from the Reuters news agency.

The employee’s detention took place back in March around the same time as a raid on US consultancy Mintz’s Beijing office in which several of that company’s local staff were arrested, according to the report.

That incident, as well as a raid on US management consultancy Bain & Co, the arrest of an executive from Japan’s Astellas Pharma and travel restrictions imposed on a senior Nomura banker, have sent chills through China’s foreign business community.