France on Tuesday called on Brunei to scrap a law due to take effect this week that would make adultery or gay sex punishable to death by stoning, joining celebrities who have spoken out against the legislation.

The new penal code under strict Sharia law, to come into force in the tiny southeast Asian sultanate on Wednesday, has already drawn fierce criticism from rights groups and the United Nations.

British pop legend Elton John and American actor George Clooney have called for a boycott of nine luxury hotels owned by Brunei in Britain, France, Italy and the United States.

"France is very worried by this decision which contradicts the international obligations undertaken by Brunei on human rights," the French foreign ministry said in a statement.

"France calls on Brunei to renounce this law and maintain its moratorium on executions," which has been in place since 1957. "France reiterates its opposition to the death penalty, in all areas and all circumstances," it added.

UN rights chief Michelle Bachelet on Monday described the new law as "cruel and inhuman", urging the government "to stop the entry into force of this draconian new penal code."

Brunei, a resource-rich former British protectorate on Borneo island with a population of about 400,000, has hit economic troubles because of declining oil prices and crude reserves.

As a result, analysts say Sultan Hassanal Bolkiah, who has ruled for over half a century, is seeking to burnish his Islamic credentials among conservative supporters.

Rights groups have meanwhile accused the sultanate of becoming the Saudi Arabia of southeast Asia, in reference to the kingdom's tough Sharia law.