BANGKOK, May 27 (Xinhua) -- Thailand's King Maha Vajiralongkorn has ordered the Royal Palaces to mourn the death of Privy Council President Prem Tinsulanonda for 21 days.

In a Royal Announcement publicized late on Sunday, the monarch has ordered the 21-day mourning period in the Royal Palaces for the 99-year-old Prem from Monday until June 17 except for June 3 which is the birthday anniversary of Her Majesty Queen Suthida.

Their Majesties the King and Queen are scheduled to attend the funeral ceremony for Prem at Benjamabophit temple on June 2, while Her Royal Highness Princess Maha Chakri Sirindhorn is set to attend on Monday.

The Royal Announcement paid a tribute to Prem for his former positions as army chief, prime minister, privy councillor, statesman and Privy Council president in the time of the late King Bhumibol Adulyadej and regent and Privy Council president in the time of the current king.

Thai government house also announced late Sunday that Prime Minister Prayut Chan-o-cha had ordered all public buildings, schools to lower Thai national flags for a 7-day period since Monday and a 21-day mourning period in the government.