Bangkok: Thailand's 88-year-old King Bhumibol Adulyadej, the world's longest reigning monarch, is in an unstable condition after receiving haemodialysis treatment, the palace said in a statement late on Sunday.
News about the king's health is closely monitored in Thailand, where King Bhumibol is deeply revered.
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, he 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.
News about the royal family is tightly controlled in Thailand, where laws protecting the royals from insult make it a crime to defame, insult or threaten the king, queen, heir to the throne or regent.