Singapore leaders yesterday remembered King Bhumibol Adulyadej as a king who had dedicated his life to improving the welfare of his people, in condolence letters over his death.

They also paid tribute to the role he played in fostering ties between Singapore and Thailand.

President Tony Tan Keng Yam, in letters to Queen Sirikit and Crown Prince Maha Vajiralongkorn, said King Bhumibol was "truly remarkable and had, throughout his long reign, worked tirelessly for the people of Thailand".

He noted that the King had "dedicated his life to improving the welfare of his people and developing the Kingdom of Thailand".

"History will remember His Majesty King Bhumibol as a great monarch, and a unifying force deeply loved and respected by the Thai people and the rest of the world," he said.

Dr Tan, who is in Norway on a state visit, also paid tribute to King Bhumibol in an interview with Singapore reporters at the end of his trip yesterday.

He said the King is "well beloved by his people and for good reasons".

He pointed to the numerous projects that the King had launched in Thailand, such as in the areas of water management, that had brought deep and far-reaching benefits to Thailand.

Recalling that he had visited some of the projects, Dr Tan said: "This has contributed to increasing the livelihoods as well as new economic activities for the Thai people, particularly those living in the rural area."

King Bhumibol, who was the longest-reigning monarch in the world, had also been a source of stability for Thailand through all its ups and downs, and political changes, said Dr Tan.

"The King has been a reference point, a rock on which Thailand can depend on. The outpouring of sadness and emotion which you can see on television that followed the announcement of his passing shows how much he is loved by all sectors of the Thai people," he said.

"His reign will be remembered for the peace and prosperity which he has brought to the kingdom of Thailand."

Prime Minister Lee Hsien Loong, in a letter to Thai Prime Minister Prayut Chan-o-cha, said Singapore would remember the role King Bhumibol played in fostering the enduring friendship between both countries.

He also paid tribute to the King's love for his people. "Throughout his long and benevolent reign, His Majesty King Bhumibol had profound compassion for his people, and ceaselessly dedicated himself to improving their well-being," he said.

Later in the afternoon, Mr Lee wrote in a condolence book for the King at the Royal Thai Embassy in Singapore: "His Majesty worked tirelessly for the people of Thailand throughout his long reign, and brought great progress to his country. The world has lost a revered monarch and great leader. Our thoughts are with the people of Thailand in their grief."

Foreign Minister Vivian Balakrishnan, in a letter to his Thai counterpart Don Pramudwinai, noted that King Bhumibol was a compassionate King who had devoted his time and energy to the people, and made many trips to the provinces and rural areas in Thailand to listen to people's concerns and help improve their lives.

Describing these travels as "inspiring", he said: "His Majesty King Bhumibol was a great blessing to the people of Thailand."

Dr Balakrishnan, who is in Bangkok for the Asean-European Union Ministerial Meeting, also signed a condolence book for the King at the Thai Ministry of Foreign Affairs.

He wrote: "Singapore stands shoulder to shoulder with our Thai friends in this sad and difficult period."