BEIJING (Reuters) - China said on Friday a Japanese citizen was being investigated for harming national security, following a similar case last month in which China said six Japanese were being questioned on suspicion of illegal activity.

“In May of this year, the relevant Chinese department put under investigation in accordance with the law a Japanese citizen on suspicion of harming China’s national security,” ministry spokeswoman Hua Chunying told reporters, without offering details.

In Tokyo, Japanese Chief Cabinet Secretary Yoshihide Suga said they had been informed by China that the person was a man in his 60s who had been detained in the northeastern Chinese province of Liaoning for “violating China’s domestic law”.

“We will continue offering appropriate support through our diplomatic establishments aboard in light of protecting Japanese nationals,” Suga said.

Liaoning shares a border with nuclear-armed North Korea.

Last month, China said it was investigating six Japanese citizens on suspicion of “illegal activities”, after Japanese media reported they may have been suspected of spying.

Relations between China and Japan have been strained for decades by the legacy of Japan’s wartime aggression.

A maritime territorial dispute over small islands in the East China Sea has in recent years added to the suspicion between the two sides.

In 2010, four Japanese nationals were detained in China on suspicion of entering a military zone and taking photographs without permission.

At least two Japanese citizens were arrested on suspicion of espionage in 2015. Last year, China said it was investigating a Japanese citizen on suspicion of endangering national security.