Thailand's ailing but much adored King Bhumibol Adulyadej cancelled plans to hold an annual audience to mark his 87th birthday Friday on the advice of his doctors, the palace said.
The king, who is the world's longest-serving monarch, has spent most of the last few months in hospital as fears over his health mount in a nation where he is seen as a unifying, father-figure throughout a turbulent six-decade rule.
"A team of royal physicians examined the king on Thursday evening... and agreed that he is not ready to grant a royal audience therefore they have recommended he cancels royal activities," the Royal Household Bureau said in a statement early Friday.
Plans to hold a grand audience and live broadcast the ceremony were also scrapped, an official at the Royal Household Bureau told AFP.
In October the king underwent an operation to remove his gall bladder after tests revealed it was swollen.
He was last seen in public in early November.
The king's birthday -- also known as "Father's Day" in Thailand -- is a public holiday and Thais traditionally wear the royal yellow as a sign of devotion to the monarch, while roads are lined with royal flags.
Elaborate celebrations were expected at the royal palace in Bangkok, where the king traditionally makes an appearance and gives a brief statement to his subjects.
The king last failed to make an appearance in 2008 for his 81st birthday celebrations following ill health.
A large crowd of well-wishers, many dressed in yellow and waving flags, gathered in the grounds of Bangkok's Siriraj Hospital where Thailand's monarch is convalescing chanting "Long Live the King!", an AFP reporter on the scene said. Some had camped out overnight.
- Anxious for the future -
Crown Prince Maha Vajiralongkorn had been expected to carry out some official ceremonies to mark his father's birthday.
Most Thais have only known King Bhumibol on the throne and anxiety over the future once his six-decade reign ends is seen as an aggravating factor in Thailand's bitter political divide.
His period as a constitutional monarch has been pock-marked by nearly 20 attempted or successful coups, the last in May which saw the army topple the elected government.
Thailand remains under martial law, a condition the arch-royalist army says is necessary to keep the peace as it vows to expunge the kingdom of corruption and reboot Thai democracy.
Critics of the military say it has used its status as the defender of the monarchy as a pretext to grab power from the elected government aligned with Thaksin Shinawatra -- the billionaire self-exiled former premier whose emergence as an electoral force in 2001 shook up Thai politics.
Thaksin's sister Yingluck was forced out as prime minister shortly before the military's May takeover.
Thailand's monarchy is protected by one of the world's strictest lese majeste laws and the army have ramped up prosecutions under the controversial legislation.
Both local and international media must heavily self-censor when covering the country's royal family.
Under section 112 of Thailand's criminal code anyone convicted of defaming, insulting or threatening the king, queen, heir or regent faces between three and 15 years in prison on each count.
Even repeating details of the charges could mean breaking the law.
A recent study by the Paris-based International Federation of Human Rights said lese majeste cases have surged since the coup, with 18 new arrests made and outstanding cases fast-tracked through the courts.
Since the coup, royal defamation cases can also be sent to military courts with no right of appeal.
On Wednesday a lawmaker from Thailand's toppled ruling party was jailed for two-and-a-half years for lese majeste.
Two weeks earlier a radio show host was jailed for five years by a military court for breaching the law.