King Bhumibol Adulyadej of Thailand, the world’s longest-reigning monarch and the object of intense devotion for many Thais, has spent a third night in hospital, underlining the atmosphere of crisis and division in the country.

Doctors said that the the condition of the King, 81, had improved since Saturday, when he was put on antibiotics and an intravenous drip after suffering fever, tiredness and loss of appetite. “In the past 24 hours His Majesty has less fever but he still has a loss of appetite,” the royal household bureau said in a statement read out on national television. “The medical team is still giving him antibiotics and nutrients.”

The King’s indisposition, after some of the most tumultuous and chaotic months in modern Thai history, is a reminder of the degree to which the country’s stability depends on his continuing survival – and of the uncertainty that is likely to follow his death.

King Bhumibol’s illness came at the end of a tense day in Thailand, and after three years of bitter division, conflict and political instability. On Saturday, tens of thousands of supporters of the deposed former prime minister, Thaksin Shinawatra, marched through Bangkok to mark the third anniversary of the military coup that ejected him from power.

“Three years after the coup, our country has slid backwards,” Mr Thaksin told supporters of the “Red Shirt” movement, the United Front for Democracy against Dictatorship (UDD), via a videolink from his exile in an unidentified foreign country. “There is no justice in society. The longer this government stays, the bigger the disaster is for the country. Give me just six months as prime minister, and I will bring this country back to normal.”

Meanwhile, members of the People’s Alliance for Democracy, who oppose Mr Thaksin, mounted a violent display of nationalist fervour at a Buddhist temple on a disputed area of border with Cambodia. Dozens of people were injured, after the “Yellow Shirts” fought with Thai police and local villagers.

Abhisit Vejjajiva, the Prime MInister, visited the Siriraj Hospital in Bangkok over the weekend to offer wishes for the King’s recovery, and assured Thais that the treatment was routine. “His Majesty's condition is not a problem,” he said. There is no reason to doubt this, but the timing of the King’s illness is bound to provoke anxiety among Thais.

In the past few years millions of Thais have taken to dressing in yellow, the royal colour, in honour of the King. Thai towns and cities display posters of Bhumibol and his Queen, Sirikit, every few hundred yards. Along with his family, he is protected by a harsh lèse majesté law which punishes any perceived insult to the monarchy. A female opposition activist was sentenced last month to 18 years in prison for this crime.

Bhumibol is also respected for his occasional, but influential, interventions in Thai politics when he has forced compromise between squabbling politicians and appealed for national unity.

His son, the Crown Prince Maha Vajiralongkorn, has been married three times and in the past two years scandalous film footage has been distributed on the Internet and on clandestine CDs, featuring him and his current wife, Princess Srirasmi.

An Australian writer, Harry Nicolaides, spent five months in prison for a novel thaty referred to the romantic entanglements and intrigues of the Crown Prince, before he received a royal pardon. A biography of Bhumibol by the American writer, Paul Handley, which also touches on the taboo subject, is denied distribution in Thailand.

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