(CNN) -- A court in Indonesia on Monday rejected the appeal of a 56-year-old British grandmother sentenced to death for drug trafficking on the island of Bali.
A spokesman for the Denpasar High Court told CNN that it upheld the sentence handed down by the Denpasar District Court in January but gave no reasons for the decision.
Prosecutors in Bali had asked for a 15-year sentence for Lindsay June Sandiford, who was arrested last May carrying what officials said was cocaine worth an estimated $2.6 million.
Sandiford, from northeast England, was found to have blocks of cocaine weighing 4.7 kilograms (10.4 pounds) in her suitcase when she arrived on the island, the court heard during her original trial.
Britain's Foreign and Commonwealth Office expressed its disappointment at Monday's decision.
"The UK strongly opposes the death penalty and has repeatedly made representations to the Indonesian government on this matter. We will continue to provide consular assistance to her at this difficult time."
The UK-based group Reprieve, which works to secure the human rights of prisoners around the world, said neither Sandiford nor her lawyer had yet been formally informed of the outcome of the appeal.
The next step would be to file an appeal with the Supreme Court, Reprieve investigator Zoe Bedford said.
But, she said, "Lindsay's lawyer has exhausted all the funds which were kindly donated by the public and Lindsay's friends and family to cover his expenses for the appeal to the High Court. If her appeal has been unsuccessful, Lindsay will now need to somehow raise the funds for legal representations for an appeal to the Supreme Court."
According to the original trial judges, the defendant showed no regret for what she did, Indonesian state news agency Antara reported.
"We were surprised by the decision, because we never expected the death penalty," Ezra Karo Karo, a lawyer acting for Sandiford, told Antara in January.
He said the judge did not consider mitigating circumstances in his client's case, such as that she acted under the threat of violence to her family, the news agency reported.
Indonesia, the world's most populous Muslim nation, has strict laws against drug trafficking.
The head of Bali's Customs and Excise Agency monitoring division, Made Wijaya, warned at the time of her arrest that Sandiford could face execution if convicted.
"The main reason is because narcotics can massively endanger the young and, thus, whoever is caught with drugs should be severely punished. If three people can consume one gram of cocaine, then this operation has potentially saved up to 14,000 lives," he said.
Reprieve has previously said Sandiford was a vulnerable person who should not have been sentenced so harshly.
"Lindsay has always maintained that she only agreed to carry the package to Bali after receiving threats against the lives of her family," said Harriet McCulloch of Reprieve in January.
"She is clearly not a drug kingpin -- she has no money to pay for a lawyer, for the travel costs of defense witnesses or even for essentials like food and water."
The High Court spokesman said the appeal decision was made on April 2 but still needs to be ratified by the lower court.
CNN's Kathy Quiano contributed to this report.