Prosecutors in Saudi Arabia have referred detained women's rights activists to trial, saying those charged "enjoy all rights preserved by the laws in the kingdom" after them being reportedly tortured in custody.

Prosecutors issued the statement late on Friday night, referring to their earlier June statement that marked the activists' arrest just before Saudi Arabia granted women the right to drive.

Prosecutors alleged those arrested had the "aim to undermine the kingdom's security, stability and national unity."

Several people with knowledge of their arrest have told The Associated Press that some of the women detained have been subjected to caning, electrocution and others were also sexually assaulted. All spoke on condition of anonymity for fear of reprisal and to protect personal details about the detainees.

The Saudi government did not respond to questions about the women's cases early on Saturday.

The women, who include activists in their 20s as well as mothers, grandmothers and retired professors, have been accused of vague national security violations in connection to their human rights work. Canadian criticism of the arrests saw Saudi Arabia cut diplomatic ties to Ottawa.

Human rights groups have criticised the arrests, which come amid a series of crackdowns led by Saudi Crown Prince Mohammed bin Salman, the son of King Salman.

"The Saudi prosecution is bringing charges against the women's rights activists instead of releasing them unconditionally," said Michael Page, deputy Middle East director at Human Rights Watch.

"The Saudi authorities have done nothing to investigate serious allegations of torture, and now, it's the women's rights activists, not any torturers, who face criminal charges and trials."

The kingdom also faces widespread international criticism over the assassination of Washington Post columnist Jamal Khashoggi at the Saudi Consulate in Istanbul in October 2018, allegedly by members of Prince Mohammed's entourage, as well as over its yearslong war in Yemen.