Human rights groups on Tuesday denounced an 11-year prison term handed down by a counterterrorism court to a Saudi fitness instructor and women's rights activist.

The judgement against 29-year-old Manahel al-Otaibi was issued on January 9 but only made public "weeks later" in a Saudi submission to United Nations special rapporteurs inquiring about the case, Amnesty International and ALQST said in a joint statement.

Otaibi, who is also a blogger, was arrested in November 2022.

Rights groups contend that law enforcement targeted her for challenging Saudi male guardianship laws and requirements for women to wear the customary body-shrouding abaya robe.

The Saudi submission to the UN, dated January 24 and seen by AFP on Tuesday, says, however, that Otaibi "was convicted of terrorist offences that have no bearing on her exercise of freedom of opinion and expression or her social media posts".

The submission does not provide details about the "terrorist offences".

The Saudi government said on Tuesday it would look into a request for comment submitted by AFP.

Tuesday's joint statement from the rights groups said Otaibi "was forcibly disappeared" between November last year and mid-April, when she was able to contact her family again.

Her older sister Foz al-Otaibi, followed by 2.5 million people on the social media app Snapchat, "faces similar charges, but fled Saudi Arabia fearing arrest after being summoned for questioning in 2022," the statement said.

Foz told AFP on Tuesday that the family only learned of Manahel's 11-year sentence through the Saudi UN submission.

"I feel very shocked," she said, adding that Manahel "did not do anything that deserved to be imprisoned for up to 11 years."

The rights groups' statement called for Manahel al-Otaibi's release.

"Saudi authorities must immediately and unconditionally release Manahel al-Otaibi and all those currently detained in the kingdom for the peaceful exercise of their human rights," said Lina al-Hathloul, head of monitoring and communication for ALQST.

"Pending al-Otaibi's release, the authorities must ensure her safety and access to adequate health care."

Saudi Arabia, the world's biggest crude oil exporter, has long been associated with the repression of women because of former rules such as a ban on driving and a requirement to wear abaya robes.

While those restrictions have been lifted, human rights activists say a personal status law that took effect in 2022 still discriminates against women when it comes to matters concerning marriage, divorce and child-rearing.

And women, including prominent activists, have been rounded up in a wide-reaching campaign against dissent.

Among them are two women who in 2022 received decades-long prison sentences for social media posts critical of the government.