Australian woman Cassie Sainsbury faces up to 30 years in a Colombian prison after a judge threw out her six-year plea deal over cocaine-trafficking charges.

The plea deal, struck with prosecutors in July, would have seen her serve a reduced prison term in exchange for accepting responsibility for drug trafficking and naming those behind the smuggling ring.

The 22-year-old was arrested in the Colombian capital’s airport in April with almost six kilograms of cocaine hidden in her luggage.

After Ms Sainsbury sensationally claimed she was forced to carry the drugs in the face of death threats at a sentencing hearing last month, Judge Sergio Leon adjourned the session to consider the development.

On Thursday (AEST) Judge Leon told a Bogota court that in the light of Ms Sainsbury’s testimony, he could not approve her plea deal reached with prosecutors.

Under Colombian law, Ms Sainsbury would have had to admit to willingly attempting to smuggle cocaine out of the country to be eligible for a deal.

A sobbing Ms Sainsbury was led from the court and returned to El Buen Pastor women’s prison in Bogota. She will reappear to court on a yet-to-be-determined date.

In a written statement to the court, Ms Sainsbury said drug traffickers told her she was being watched and could not leave Colombia.

.@sarahblakemedia: the judge had 'no option' but to reject Cassie Sainsbury's plea deal. MORE: https://t.co/nhO94Nvs8C pic.twitter.com/LBOmxAj8Kb

— Sky News Australia (@SkyNewsAust) August 9, 2017

She said she only put the drugs in her suitcase because a man with a gun, she named as Angelou, had threatened her and her family.

Ms Sainsbury told the court she initially thought she was carrying documents in exchange for $10,000.

The prosecution has up to 120 days to present evidence proving Ms Sainsbury’s intent to smuggle drugs for money.

Ms Sainsbury’s lawyer, Orlando Herran, claimed the judge did not believe the prosecution had a strong case.

He said he would ask the prosecutor to drop the charges due to a lack of evidence.

Despite warnings that the new claim of death threats during a drama-filled sentence hearing two weeks ago would destroy her chance of a reduced sentence, Mr Herran told reporters ahead of Thursday’s hearing she was maintaining her story.

Cassie Sainsbury with the alleged drug haul at Bogota’s El Dorado airport. Photo: AAP

“As the defence, we don’t have the resources of the prosecution,” he told Fairfax media outside the court.

“At the moment, we only have Cassandra’s words about the threat.

“Cassandra doesn’t have the personal resources for a private investigator to prove the threat.”

Mr Herran has applied for funding from the federal government.

Ms Sainsbury was supported in court by mother Lisa Evans and fiance Scott Broadbridge, as well as Australian consular officials.

Ms Sainsbury was intercepted by authorities and arrested at El Dorado International Airport, where she was allegedly carrying 5.8 kilograms of cocaine hidden inside her suitcase.

The former gym owner, whose family claimed she was in Colombia on a working holiday, was preparing to board a flight to London on her way back to Australia when she was arrested.

Colombian police said the drugs were divided into 18 plastic bags and hidden inside boxes of headphones, which she claimed were bought as gifts for her bridal party guests.

Jorge Mendoza, Anti-Narcotic Police Ports and Airports director, said police were given a tip-off that Ms Sainsbury may have been carrying drugs out of the country.

He estimated the drugs were worth about US$1 million (A$1.3 million).

– with ABC and AAP