Thailand's revered but ailing King Bhumibol Adulyadej has been placed on antibiotics following a fresh blood infection, the palace revealed Monday, amid public concern over the health of the world's longest serving monarch.

The 87-year-old king, who is perceived as a near-deity by many Thais, has been in Bangkok's Siriraj Hospital since being re-admitted in May, but information on his condition has been scarce.

In a statement released late Monday the Royal Household Bureau said King Bhumibol had come down with a high fever, chills and low blood pressure last Thursday.

"The result of blood checks found that he had an infection in his blood. The result of a chest X-ray found that his right lung was inflamed," the palace said.

"As a result the doctors have given him some antibiotics and saline drip. They have also given him some oxygen," the statement added, saying his blood pressure and fever has since stabilized.

King Bhumibol has been in and out of hospital for much of the last two years and rarely makes public appearances.

A day before his latest bout of illness the palace released footage of the wheelchair-bound monarch visiting a shop near the hospital where he is convalescing as subjects on their knees chanted "Long live the King".

Last month the palace said he had recently been treated for "water on the brain" and a chest infection.

Fears over Thailand's future among competing elites as Bhumibol's reign enters its twilight years are seen as a motivating factor behind a decade of political turmoil in the kingdom.

Since 2006, the nation has witnessed two coups, the removal of three prime ministers by the courts and several rounds of street protests that have often ended in violence.

Ultra-royalist generals seized power in a coup in May last year after weeks of protests against the civilian government of Yingluck Shinawatra, whose family and their proxies have won every election since 2001.

The Shinawatras are loathed by the royalist elite who accuse them of widespread corruption and subverting the kingdom's political status quo.

Outside of official statements the king's health is a taboo topic.

The Thai monarchy is shielded by one of the world's toughest lese majeste laws and prosecutions have increased dramatically since the military took over.

A man was jailed for 30 years last month for "insulting" the monarchy on Facebook, in one of the toughest known sentences for royal defamation. The same day a woman received a 28-year jail term for the offense.

Media have to routinely self-censor when reporting on the monarchy for fear of falling foul of the broadly worded law, which carries up to 15 years in jail for each count of insulting the king, queen, heir or regent.

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