A Swiss man who spray-painted several portraits of Thailand's king has been sentenced to ten years in prison.

Oliver Jufer, 57, received a rare prison term after violating the southeast Asian nation's tough lese-majeste laws.

He could have faced a maximum of 75 years, but the judge reduced the term on account of Jufer's guilty plea.

Judge Pitsanu Tanbuakli said defamation of the king was 'a most serious crime'.

The long-time resident of Thailand was arrested in the northern city of Chiang Mai after defacing several portraits of 79-year-old King Bhumibol Adulyadej, who is revered by most Thais.

Police believe Jufer was drunk and angry that alcohol sales were ended early on 5 December in honour of the King's birthday.

The Swiss embassy in Bangkok said it respected the Thai courts and noted that 'the application of the Thai penal code in cases of crimes of lese majeste is rigorous'.

Thailand is one of the few countries which strictly prosecutes anything deemed to demean the royal family.

Other foreigners have violated the law in the past, but jail terms are rare.

CONSTITUTIONAL MONARCHY

Many attribute the relative calm of last year's coup in Thailand to the King's influence.

The military junta that ousted former prime minister Thaksin Shinawatra from power even sought the King's formal blessing.

King Bhumibol, who was born in Massachusetts and educated in Jufer's home country of Switzerland, celebrated 60 years on the throne in 2006.

He is considered to be pro-democracy and a champion of the poor.

Giant portraits of the King and Queen adorn buildings across the country.

Many Thais wear yellow shirts, especially on Mondays, the day of his birth.

Some legal experts say it may be time to reform the lese majeste law and the King said in 2005 that he was not above criticism.

But few Thais even dare to call for changes to the law.

'Those who do so will be deemed as showing their disloyalty to the revered monarch, which is a severe accusation', said Somchai Preechasinlapakul, dean of the Faculty of Law at Chiang Mai University.