TOKYO — China has detained two Japanese citizens suspected of smuggling items prohibited from import or export, a Japanese official said Wednesday, in a case reportedly linked to rare earths, critical materials that are largely controlled by Beijing.

Japans’s Chief Cabinet Secretary Minoru Kihara told reporters in Tokyo that Japanese consular offices in Shenyang and Dalian were notified by the Chinese customs authorities that the two Japanese nationals were detained, one on May 18 and another one a week later, “in the same alleged case.”

Kihara said the two were in good health, but refused to give further details about them or the case, on grounds of their privacy and the ongoing investigation.

In Beijing, Chinese Foreign Ministry spokesperson Guo Jiakun confirmed the detention of two Japanese citizens for violating Chinese laws, but did not give any details of the case.

“What we would like to emphasize is that the Japanese side should educate and remind Japanese citizens and enterprises in China to abide by Chinese laws and regulations,” Guo told a daily briefing.

Kyodo News agency reported that the two Japanese nationals are employees of a major Japanese machinery maker, and one of them works at its Chinese subsidiary. Their alleged attempt to take materials related to rare earths might have been considered illegal, Kyodo said.

The detention comes five months after Beijing banned exports to Japan of dual-use goods that can have military applications. China says the export control does not affect commercial goods, but trade data show exports of rare earths magnets from China have declined since.

Ties between the two major Asian economies have been strained for months.

Bilateral relations deteriorated when Japanese Prime Minister Sanae Takaichi’s suggested late last year that Chinese action against Taiwan, a self-governed island state Beijing considers its own territory, could justify Japanese military action. Previous Japanese leaders had maintained strategic ambiguity on the matter of Taiwan.

In another case that caused strains, a Japanese man who had been detained since March 2023 was sentenced last year to three and a half years in prison in China on espionage charges.

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Associated Press writer Ken Moritsugu in Beijing contributed to this report.