Indonesia's highest court has upheld the death sentence for a British woman convicted of smuggling $2.5 million worth of cocaine into the resort island of Bali, a court official has said.

A three-member judge panel unanimously rejected Lindsay June Sandiford's appeal, the Supreme Court spokesman Ridwan Mansur said on Friday.

The 57-year-old woman was found guilty in January by a district court for smuggling 4.79kg of cocaine into Bali and sentenced to face a firing squad.

She lost an appeal three months later after the Bali High Court upheld the lower court's ruling.

A spokesman for the British embassy in Jakarta, Adam Rutland, said consular assistance would continue to be provided to Sandiford and her family.

"We are aware that Lindsay Sandiford's appeal to the Indonesian Supreme Court has been denied," Adam Rutland, spokesman for the British Embassy in Jakarta, said in an email.

"In line with our strong opposition to the death penalty in all circumstances, we will consider how to support any application for judicial review or clemency that Lindsay Sandiford chooses to make."

Prosecutors had initially sought 15 years in prison for Sandiford, but the court surprised many by issuing a death sentence.

Under Indonesian law, Sandiford still has the opportunity to avoid execution, a judicial review of the top court's decision or a presidential pardon. But death row convicts in Indonesia rarely have their sentences reduced.

The British woman was sentenced to death after cocaine was found in her suitcase as she arrived on a flight from Bangkok in May last year.

Four other defendants - three British and an Indian - connected to the case were sentenced to jail terms ranging from one to six years.

Police said she was at the centre of a drugs-importing ring involving three other Britons.

Sandiford said she was forced to transport the drugs to protect her children whose safety was at stake. The court, however, rejected that argument.