BEIJING, China: During his talks with Chinese Foreign Minister Qin Gang, Japan's Foreign Minister Yoshimasa Hayashi has demanded the early release of an employee of Japanese pharmaceutical company Astellas Pharma, who was detained in Beijing last month over alleged spying allegations.

He also raised "strong concern" about Beijing's escalating military activity near Taiwan and around Japan.

As tensions rise between the two countries, Hayashi's two-day visit to China is the first by Japan's first diplomat in more than three years.

He also met Chinese Premier Li Qiang and top diplomat Wang Yi.

Talking to reporters, Hayashi stressed the importance of peace and stability in the Taiwan Strait, and raised "serious concern" about China's increasingly assertive activity in the East and South China seas.

He also expressed grave concern about Beijing's increased joint military activity with Russia around Japan, urging China to act responsibly for global peace amid Moscow's invasion of Ukraine.

The two ministers agreed to work together in achieving "a constructive and stable relationship," as agreed between their leaders in November, Hayashi said.

The ministers also agreed to improve communication on regional security issues, and welcomed the establishment of a defense hotline last week and the resumption of defense talks, he added.

China's assertive activity in the East China Sea and the recent detention are "a stumbling block for promoting economic and people-to-people exchanges," Hayashi separately told Wang.

In recent years, tensions have risen between Tokyo and Beijing, as Japan considers China's growing influence in the region a threat to its security and economy.

In response, Qin warned Japan about its involvement in Taiwan, stressing that Tokyo should not interfere and "undermine China's sovereignty in any way."

"The Taiwan issue is at the core of China's core interests and concerns the political foundation of China-Japan relations," he added.

While Japan does not formally recognize Taiwan, both sides have strong unofficial relations.

Qin also criticized Japan over its new export controls of semi-conductor manufacturing equipment, after the US imposed similar sanctions.

Japan had acknowledged that it consulted with Washington on its own regulations.

In response, Hayashi said the measures do not target any specific country.