Thailand's 88-year-old King Bhumibol Adulyadej, the world's longest reigning monarch, is in an unstable condition after receiving haemodialysis treatment, according to a statement issued by the palace.
News about the king's health is closely monitored in Thailand, where King Bhumibol is widely revered, and the wording of palace statements on his health is intensely scrutinised.
Strict laws protecting the royal family also stifles public discussion of the king's health.
It is unusual for the palace to state that the king's health is not stable. Statements on his health are usually issued after the monarch's condition shows improvement or when he is recovering from an illness.
The king has been treated for various ailments over the past year at Bangkok's Siriraj Hospital - his home for much of the past year - and was last seen in public on January 11, when he spent several hours visiting his palace in the Thai capital.
Anxiety over the king's health and an eventual succession has formed the backdrop to more than a decade of bitter political divide in Thailand that has included two military coups and often-violent street demonstrations.
Sunday's statement was the second health bulletin this month after the palace said on October 1 that the king was recovering after a respiratory infection.
On Saturday, the king was given haemodialysis - a way of cleansing the blood of toxins, extra salts and fluids - which made his blood pressure drop occasionally, the palace said.
Doctors gave him some medicine and put him on a ventilator to bring his blood pressure back to normal, it said.
They continue to monitor his condition closely, the statement said.
"His condition has yet to stabilise," the palace said.
