China has detained two Japanese citizens on suspicion of smuggling prohibited items, Japanese and Chinese officials confirmed on Wednesday, in a case reportedly linked to rare earth materials.

Japan's Chief Cabinet Secretary Minoru Kihara said Chinese customs authorities informed Japanese consular offices in Shenyang and Dalian that one Japanese national was detained on May 18 and another a week later in connection with the same case.

Kihara said both individuals were in good health but declined to provide further details, citing privacy concerns and the ongoing investigation.

In Beijing, Chinese Foreign Ministry spokesperson Guo Jiakun confirmed that two Japanese citizens had been detained for violating Chinese laws, but did not elaborate on the allegations.

Guo urged Japanese citizens and companies operating in China to comply with Chinese laws and regulations.

Japan's Kyodo News agency reported that the two detainees are employees of a major Japanese machinery manufacturer, with one of them working at the company's Chinese subsidiary. According to the report, the case may involve an attempt to take materials related to rare earths out of China, an act that could be deemed illegal under Chinese regulations.

The detentions come five months after Beijing imposed export restrictions on dual-use goods to Japan that could have military applications.

Although Chinese authorities have said the export controls do not affect commercial products, trade data indicate that China's exports of rare-earth magnets have declined since the restrictions were introduced.

Relations between China and Japan have been under strain in recent months.

Tensions escalated after Japanese Prime Minister Sanae Takaichi suggested late last year that Chinese military action against Taiwan could justify a Japanese military response. Previous Japanese governments had maintained a policy of strategic ambiguity regarding Taiwan, which Beijing considers part of its territory.

Another source of friction has been the detention of a Japanese man on espionage charges. The man, who had been held in China since March 2023, was sentenced last year to three and a half years in prison.