China said Wednesday it has arrested two Japanese citizens for suspected spying, a move likely to strain already tense ties between Asia's two largest economies.

The detentions -- the first since 2010 involving Japanese on such charges -- come as relations remain clouded by disputes over islands and Tokyo's wartime history, despite close trade links.

In Tokyo Japan's top government spokesman said the two people were held separately in May, one in the northeastern province of Liaoning and another in the eastern province of Zhejiang.

The spokesman, Chief Cabinet Secretary Yoshihide Suga, said he believed they were private citizens and Japanese diplomats had "offered support".

Japan does not engage in spying, he had told a briefing earlier in the day.

China's foreign ministry said the two Japanese were arrested "on suspicion of carrying out espionage activities".

Asked why they had been held for months without any public statement, ministry spokesman Hong Lei told a regular briefing in Beijing that China had dealt with the case "in accordance with the law".

His statement came a week after China said it was holding a US businesswoman on suspicion of spying.

Supporters of the woman, Sandy Phan-Gillis, said she had been held for six months but denied she had any links to espionage.

Japan's Asahi newspaper said the two Japanese are being held on a string of charges including violating China's anti-espionage law introduced last year.

One was detained near the North Korean border while the other was picked up close to a military facility, public broadcaster NHK and the Asahi cited sources as saying.

Kyodo News said both are in their 50s.

The detentions are thought to be the first of their kind since China in 2010 held four Japanese men in the northern province of Hebei.

The group were employees of Tokyo-based construction company Fujita, which said they had been visiting the city of Shijiazhuang to prepare a bid for a project to dispose of chemical weapons left in China by invading Japanese forces in the 1930s.

The group were later released and sent back to Japan after they admitted filming in a military area. They said they had no idea they were in a restricted zone.

Japan and China are locked in conflict over disputed islands in the East China Sea, which in recent years sparked large-scale anti-Japanese protests in China.

Japan's brutal occupation of parts of China before and during World War II also remains a sore point, with Beijing accusing Tokyo of failing to atone for its past.

China last month said Japan missed an opportunity to offer a "sincere apology" for its World War II aggression, after Japanese Prime Minister Shinzo Abe reiterated Tokyo's past expressions of "deep remorse" over the conflict.

But ties have been seen as thawing somewhat in recent months, with China's President Xi Jinping holding a meeting with Japan's Prime Minister Shinzo Abe in April.