BANGKOK, Thailand (CNN) -- A pregnant British woman facing possible execution in Laos will go on trial this week, the country's foreign affairs ministry said Monday.

Samantha Orobator became pregnant in prison, according to a spokeswoman for rights group Reprieve.

Samantha Orobator "is facing death by firing squad for drug trafficking," said Clare Algar, executive director of Reprieve, a London-based human rights group.

Orobator, 20, was arrested on August 5, said Khenthong Nuanthasing, the Ministry of Foreign Affairs spokesman.

She was alleged to have been carrying just over half a kilogram (1.1 pounds) of heroin, Reprieve lawyer Anna Morris told CNN by phone from Vientiane, the Laotian capital. "For that amount of heroin the sentence is normally the death penalty," she said.

Orobator's mother Jane found out in January her daughter was pregnant -- more than four months after she was arrested, her mother said.

Jane Orobator heard the news from the British Foreign Office, which has been monitoring the case, the mother told CNN by phone from Dublin, where she lives.

She cannot believe her daughter was involved in drug trafficking and was surprised to learn she was in Laos, she said.

"I don't know" what she was doing there, she said. "The last time she spoke with me, she said she was on holiday in London and she would come to see us in Dublin before returning to the U.K. in July.

"She is not the type of person who would be involved in drugs," she added.

Reprieve is worried about her health, especially given her pregnancy, Anna Morris said.

"She became pregnant in prison. We are concerned that it may not have been consensual, and we are concerned that someone who finds herself in prison at 20 is subject to exploitation," she said.

She is due to give birth in September, the lawyer added.

Reprieve sent Morris from London to Laos to try to help Orobator, Algar said.

The lawyer arrived there on Sunday and is hoping to visit Orobator on Tuesday, her boss at Reprieve said. A British consul has also arrived in the country.

"Reprieve heard about her case two weeks ago. We had thought yesterday the trial was going to start today," Algar said Monday. "We have now heard from Anna that it is not going to."

"I am the first British lawyer who has asked for access to her," Morris said. "She needs to have a local lawyer appointed to her. We are pressing very hard for the local authorities to appoint one."

She said it was normal in the Laotian justice system for a defendant to get a lawyer only days before a trial.

The last execution in Laos was in 1990, the foreign affairs spokesman said.

British Foreign Office Minister Bill Rammell issued a statement about Orobator on Saturday.

"The British Government is opposed to the use of the death penalty in all circumstances. We have made the Laos authorities aware of this at the highest levels in Samantha's case," he said.

"We are paying close attention to her welfare and are in regular contact with the Laotian authorities about her case. British Embassy officials, including the Ambassador, have visited her six times since her arrest," he said.

"In addition, Britain's consular representatives in Laos, the Australian Embassy, including the Australian Embassy doctor, have visited Samantha 10 times on our behalf," he said.

There is no British Embassy in Laos. A British vice-consul arrived in the country this weekend, the Foreign Office said Monday.

Rammell plans to raise the Orobator case with the Laotian deputy prime minister this week, he said.

Samantha Orobator was born in Nigeria and moved to London with her family when she was 8, her mother said.

CNN's Kocha Olarn contributed to this report.

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