A Saudi woman given 34 years in prison for tweets critical of the government knew people were informing on her but did not take it seriously, a friend said Thursday.

Salma al-Shehab, a member of the Shiite minority in the Sunni-ruled kingdom, had been studying for a doctorate in Britain and was arrested in January 2021 while on holiday.

On August 9 she was sentenced to 34 years in jail for aiding dissidents seeking to "disrupt public order" in the kingdom by relaying their tweets.

A friend of Shehab, who asked not to be identified for her own security, said she had not taken threats of denunciation seriously.

"We discussed people harassing her on Twitter and reporting her tweets to the security services online," the friend told AFP.

"She didn't think the authorities would be interested in someone with less than 2,000 followers," she added.

Shehab now has around 3,000 followers on Twitter.

A mother of two and a PhD candidate at Britain's University of Leeds, School of Medicine, she was also banned from travelling abroad for a further 34 years as part of the sentence.

The oil-rich Gulf state has cracked down on rights activists, many of whom have been jailed and banned from travel.

Women's rights activists have also been targeted.

The crackdown increased after Crown Prince Mohammed bin Salman became Saudi Arabia's de facto ruler in 2017.

The authorities have made available an app called "Kollona Amn" (Arabic for "We are all security") which allows "all citizens and residents in Saudi Arabia to play the role of police officer".

It is used to report accidents or crimes -- but can also be a tool to denounce political opponents.

Shehab tweeted mostly about women's rights in the conservative country.

She was jailed just weeks after US President Joe Biden visited Saudi Arabia, a controversial trip because of the kingdom's human rights record.

US State Department spokesman Ned Price told reporters on Wednesday that Washington regularly raised the issue of human rights with Riyadh.

"Exercising freedom of expression to advocate for the rights of women should not be criminalised," he said.

Rights group Amnesty International has called for Shehab's immediate and unconditional release. It described her jailing as "outrageous".

On its website, the University of Leeds said in a statement it was "deeply concerned" by the development, "and are seeking advice on whether there is anything we can do to support her".