A Chinese employee of a Japanese trading company operating in China has been detained by the country's authorities on suspicion of leaking information related to rare metals, sources familiar with bilateral relations said Sunday.

A Chinese worker responsible for rare metals at a state-owned firm has also been detained, the sources said, as the Communist-led government has been stepping up export controls on the materials essential for cutting-edge technologies.

The two Chinese individuals were detained in March, the sources said. The allegations against them have not been disclosed.

The Japanese trading company specializes in dealing with rare metals in China, while the state-owned firm is involved in the entire process from mining to sales. They have a trading relationship, the sources said.

In recent years, many countries, including China and the United States, have developed strategies to ensure a stable supply of rare metals used in the production of semiconductors and electric vehicles for economic security.

Photo taken in July 2020 shows a building housing a rare metal-related company in Baotou in China's Inner Mongolia Autonomous Region. (VCG/Getty/Kyodo)

Related coverage:

China to curb exports of some graphite used for battery production

U.S. says China set to have over 1,000 nuclear warheads by 2030