Britain's Queen Elizabeth II has sent a birthday message to His Majesty the King wishing him health and happiness.
"It gives me great pleasure to send my warmest congratulations to Your Majesty on the occasion of your 87th birthday," she said.
"The relationship between our two countries has lasted over 400 years, built on the enduring friendship between our people.
"I wish Your Majesty good health and happiness."
Russian President Vladimir Putin also sent a birthday message to the King.
"It is with satisfaction that I register the high level of the Russian-Thai relations which are based on long-time traditions of friendship and mutual respect," he said.
"I am confident that further strengthening of constructive bilateral cooperation in various fields fully corresponds to the interests of our peoples and goes in line with efforts to ensure peace, stability and security in the Asia-Pacific region.
"I wish you, Your Majesty, good health and happiness as well as well-being and prosperity to all your citizens."
United States President Barack Obama sent his good wishes to His Majesty the King on Thursday.