The monarchies — two of a handful remaining in Asia — have maintained close ties. Bhumibol first visited Japan in 1963, touching off a decades-long friendship with numerous visits back and forth, most recently a visit by Akihito to Thailand in 2006.

Akihito, accompanied by his wife, Empress Michiko, was to lay wreathes and sign a condolence book at the Grand Palace in Bangkok before meeting with King Vajiralongkorn Bodindradebayavarangkun, who ascended the throne after the death of his widely revered father in October.

The emperor's two-day visit to Bangkok comes as Thailand tilts closer to China, Japan's main rival in East Asia.

Thailand and Japan have traditionally enjoyed close relations, unburdened by the legacy of World War II that has complicated Japan's relations with other Asian countries. After a brief struggle, Thailand formally became Japan's ally through much of the war, suffering little of the destruction wrought on others like China, Myanmar and the Philippines.

But following a 2014 coup, Thailand's Western allies cut back on assistance, pushing the country's ruling military junta closer to Beijing.

"The visit is symbolic of Japan's interest in boosting Japanese-Thai relations at a time when China seems to enjoy favor in Bangkok," said Paul Chambers, research director at the Institute of Southeast Asian Affairs.

Popular

Government to permanently relocate 10,000 people after Ruang eruptions

Kokubo's injury time penalty save secures title for Japan

Residents fear for safety as Mount Ruang volcano erupts