On his first visit to China since becoming Japan's top diplomat earlier this year, Iwaya told Wang that Tokyo was "closely monitoring the Taiwan situation and recent military developments", according to his foreign ministry.
Meeting with Wang at Beijing's opulent Diaoyutai State Guesthouse, he also "expressed serious concerns over the East China Sea situation, including around the Senkaku Islands (and) China's increasing military activity," Tokyo said.
Iwaya in addition called for the "swift release" of Japanese nationals detained by Chinese authorities.
"Opaqueness surrounding the anti-espionage law is causing Japanese people to think twice about visiting China," he warned.
But the two ministers also agreed to work towards a visit to Japan by Wang "at the earliest possible timing next year".
Earlier, Iwaya met Chinese Premier Li Qiang and agreed to work for a "constructive and stable" relationship, Japanese news agency Kyodo said.
China and Japan are key trading partners, but increased friction over disputed territories and military spending has frayed ties in recent years.
Beijing's more assertive presence around disputed territories in the region, meanwhile, has sparked Tokyo's ire, leading it to boost security ties with key ally the United States and other countries.
Tense ties
In August, a Chinese military aircraft staged the first confirmed incursion by China into Japanese airspace, followed weeks later by a Japanese warship sailing through the Taiwan Strait for the first time.
Beijing's rare test launch of an intercontinental ballistic missile into the Pacific Ocean in late September also drew strong protests from Tokyo, which said it had not been given advance notice.
Tensions between the two sides also flared last year over Japan's decision to begin releasing into the Pacific Ocean some of the 540 Olympic swimming pools' worth of reactor cooling water amassed since the 2011 tsunami that led to the Fukushima nuclear disaster -- an operation the UN atomic agency deemed safe.
China branded the move "selfish" and banned all Japanese seafood imports, but in September said it would "gradually resume" the trade.
On Wednesday, the two ministers affirmed their support for that plan.
China imported more than $500 million worth of seafood from Japan in 2022, according to customs data.
Japan's brutal occupation of parts of China before and during World War II remains another sore point, with Beijing accusing Tokyo of failing to atone for its past.
Visits by Japanese officials to the Yasukuni shrine that honours war dead -- including convicted war criminals -- regularly prompt anger from Beijing.
