By Amy Sawitta Lefevre and Aukkarapon Niyomyat
BANGKOK (Reuters) - The health of Thailand's 88-year-old King Bhumibol Adulyadej, the world's longest reigning monarch, has "overall not yet stabilized", the palace said on Wednesday.
The statement from the palace follows one on Sunday saying the king was in an unstable condition after receiving haemodialysis treatment, which is used to cleanse the blood of toxins, extra salts and fluids.
A Reuters reporter at Bangkok's Siriraj Hospital said all four of the king's children, including Crown Prince Maha Vajiralongkorn, visited him on Wednesday.
"On Oct. 11 his blood pressure lowered and breath quickened," the palace said. The king's health has "overall not yet stabilized," it said.
Several hundred people gathered at the hospital, where the revered king has been for much of the past year, to pray for him.
The government had earlier urged people not to listen to rumors on social media about "situations", saying they should await official announcements.
During his seven decades on the throne the king, who is seen as a unifying force, has intervened when events threatened to plunge Thailand into crisis.
He has been treated for various ailments over the past year and was last seen in public on Jan. 11, when he spent several hours visiting his palace in the capital, Bangkok.
Prime Minister Prayuth Chan-ocha, who is also head of the ruling junta, canceled an official engagement in Chonburi province on Wednesday and was having an audience with the crown prince on routine government work, the foreign ministry said.
"The government spokesman has urged for the Thai public to rely on official announcements for an update on situations, rather than uncorroborated information in social media circles," it said in a statement, without referring to the king's health.
U.S. Assistant Secretary of State Daniel Russel said the U.S.-born king has been a "true friend of the United States".
"He’s a revered figure in Thailand and he's an admired figure in the United States and we hope his situation will stabilize," Russel told reporters in Washington.
Thailand has long been an ally of the United States, for decades united in opposition to the spread of communism in Southeast Asia.
The Stock Exchange of Thailand .SETI closed down 2.5 percent, its lowest since the end of May, after falling as much as 6.9 percent at one point to its lowest since March 1, led by shares in the aviation and tourism industries.
Wednesday's palace statement was the third health bulletin this month after the palace said on Oct. 1 the king was recovering after a respiratory infection.
Laws protecting the royals from insult make it a crime to defame, insult or threaten the king, queen, heir to the throne or regent.
(Reporting by Amy Sawitta Lefevre, Aukkarapon Niyomat and Pracha Hariraksapitak, additional reporting by David Brunnstrom in WASHINGTON; Editing by Robert Birsel and Angus MacSwan)