British Defense Secretary John Healey has underlined his country's close security ties with Japan amid the changing security environment.

"We are forging a golden age of defense cooperation together," Healey told reporters Friday during his visit to Japan, calling the East Asian country "our closest security ally in Asia."

His visit coincided with port calls in Japan by Britain's aircraft carrier Prince of Wales, including at the U.S. naval base in Yokosuka, Kanagawa Prefecture, near Tokyo.

Britain sought to enhance relations with partners in the Indo-Pacific region, particularly Japan, after its exit from the European Union in 2020. The stance remains the same after a change of government, as Britain is concerned about China's economic support for Russia.

A strike group with about 4,000 personnel led by the Prince of Wales departed Britain for the Indo-Pacific region in April in what Healey described as "the biggest Royal Navy deployment in a generation."

"Security in Europe is indivisible with security in the Indo-Pacific," he said. "Our nations can operate closely together in peacetime, and if we can do so in peacetime, we can do in crisis."

This visit marked the first Japanese port call by a British aircraft carrier since the one by the Queen Elizabeth in 2021.

Earlier in August, the Prince of Wales participated in a joint exercise involving six countries, including Japan and the United States, in the Pacific Ocean east of the Philippines.

During the drill, an F-35B stealth fighter based on the Prince of Wales landed on and took off from the Maritime Self-Defense Force helicopter carrier Kaga, undergoing work to be converted into a de facto aircraft carrier.

Japan and Britain are also strengthening cooperation in the joint development of next-generation fighter jets and cybersecurity measures. Healey said that the connection between the two countries is stronger than ever.

The Prince of Wales moved from Yokosuka to the Tokyo International Cruise Terminal on Thursday and was shown to the press. It is set to be opened to the public Sunday for those who have completed advance procedures.