BANGKOK (Reuters) - Thailand's King Bhumibol Adulyadej canceled a public appearance on his 87th birthday on Friday on the advice of doctors, disappointing thousands outside a hospital where he is staying, hoping for a glimpse of the world's longest-reigning monarch.
The cancellation fueled concern over the health of King Bhumibol, who is regarded as almost divine by many Thais and is widely seen as a unifying figure through years of political unrest.
It also comes at a sensitive time, six months after the army took over in a coup and amid a corruption investigation that has led to the arrest of relatives of Princess Srirasmi, the wife of the crown prince.
The king's birthday is also known as "Father's Day" in Thailand and is a holiday.
King Bhumibol was admitted to hospital in October and underwent an operation to remove his gallbladder.
"A team of royal physicians ... agreed that he is not ready to grant a royal audience and therefore doctors have recommended he cancel royal activities," the Royal Household Bureau said in a statement.
The king last appeared in public in November.
Doctors later said the king's condition was not serious and he was recovering.
"I want the public to understand that His Majesty is not sick and does not have anything serious," Udom Kachintorn, dean of the Faculty of Medicine at Siriraj Hospital, told reporters.
"This is the recovery period after illness."
Thousands gathered outside the hospital with most wearing yellow, a color associated with the monarchy. Some shouted "long live the king" while others held portraits.
"It doesn't matter whether he appears in public or not," said Thepwitoon Chim-ngog, 37. "I'm just happy that I'm here to show my loyalty."
King Bhumibol's health and anxiety over the succession have formed part of the backdrop to a complex crisis driven by rival business and political elites.
King Bhumibol carries considerable moral weight in Thailand. He has in the past used birthday speeches to comment on the state of the nation or, as in 2001, to criticize leaders of a government led by former tycoon Thaksin Shinawatra.
The king made several interventions in the 1970s and 1990s to call for calm during political upheaval. He was silent during the latest crisis, which culminated in the May 22 coup.
The military government of Prime Minister Prayuth Chan-ocha has called on all Thais to wear yellow this month to mark the birthday.
Crown Prince Maha Vajiralongkorn is expected to carry out ceremonies to mark his father's birthday.
Additional reporting by Juarawee Kittisilpa and Viparat Jantraprapaweth; Editing by Nick Macfie and Robert Birsel