Emperor Akihito will pay the first visit by a reigning Japanese monarch to Singapore, which suffered a bloody Japanese occupation, on a June trip that will also take him to Malaysia and Thailand.

Emperor Akihito and Empress Michiko will leave Japan on June 8 on Singapore's invitation to mark the 40th anniversary of the establishment of bilateral relations.

Japan captured the island city in February 1942 in the British military's biggest ever surrender. Singaporean historians say Japanese forces killed 50,000 ethnic Chinese men before surrendering in 1945.

Singapore today is a major trade and political partner of Japan. Before his coronation, Akihito visited the island-state in 1970 and on a stopover in 1981, said the Imperial Household Agency, which does not keep records of royal visits before World War II.

The royal couple plans to leave Singapore on June 10 for Ipoh in Perak before moving to Kuala Lumpur.

The emperor and empress had been due to visit Ipoh in 1991 as the Malaysian king at the time was from Perak, but they had to cancel because of bad weather and promised to reschedule the stop.

World's longest reigning monarch

They will fly to Bangkok on June 11 to attend celebrations for the 60th anniversary of the ascension to the throne of King Bhumibol Adulyadej, the world's longest reigning monarch.

Royal families from 22 nations including the kings of Sweden and Jordan are due to take part in the events, said the Thai government. The emperor and empress last visited Thailand in 1991.

The emperor is defined as the symbol of the nation under the post-World War II constitution which ended the monarch's divine status.

Emperor Akihito and Empress Michiko last year visited Saipan, a US commonwealth in the Pacific that saw bitter fighting in 1944, to mourn the dead of all countries on the 60th anniversary of the end of World War II.

The visit came amid tension with China which accuses Japan of not atoning for its war atrocities.