The sultan of oil-rich Brunei announced that tough Islamic criminal punishments would be introduced tomorrow, pushing ahead with plans that have sparked rare domestic criticism of the fabulously wealthy ruler and international condemnation.

"With faith and gratitude to Allah the almighty, I declare that tomorrow, Thursday May 1, 2014, will see the enforcement of sharia law phase one, to be followed by the other phases," the absolute monarch said in a royal decree Wednesday.

Plans for the sharia penalties -- which will eventually include flogging, severing of limbs and death by stoning -- triggered condemnation on social media sites in the tiny, sleepy sultanate earlier this year.

Confusion has swirled around implementation following the unexplained postponement of an expected April 22 start date that raised questions over whether the Muslim monarch was hesitating.

But 67-year-old Sultan Hassanal Bolkiah -- one of the world's wealthiest men -- said in his decree that the move was "a must" under Islam, dismissing "never-ending theories" that sharia punishments were cruel in comments clearly aimed at detractors.

"Theory states that Allah's law is cruel and unfair but Allah himself has said that his law is indeed fair," he said.

The monarch's wealth -- estimated three years ago at USD 20 billion by Forbes magazine -- has become legendary with reports of a vast collection of luxury vehicles and huge, gold-bedecked palaces.

The monarchy was deeply embarrassed by a sensational family feud between Hassanal and his younger brother Jefri Bolkiah over the latter's alleged embezzlement of USD 15 billion during his tenure as finance minister in the 1990s.

Court battles and exposes revealed salacious details of Jefri's un-Islamic jet-set lifestyle, including allegations of a high-priced harem of Western paramours and a luxury yacht he owned called "Tits".

Bruneians enjoy among the highest standards of living in Asia due to the country's energy wealth, with education, medicine and other social services heavily subsidised.

The sultan first proposed the sharia penal code in 1990s, and in recent years has increasingly warned of rising crime and pernicious outside influences such as the Internet. He has called Islam a "firewall" against globalisation.

He announced the implementation plans in October.

Brunei is the first country in East or Southeast Asia to introduce a sharia penal code on a national level.