Saudi Arabia on Thursday released three out of 11 women detained last year in a sweeping crackdown on activists, a close relative and London-based rights group ALQST said.

Blogger Eman al-Nafjan, Aziza al-Youssef, a retired lecturer at King Saudi University, and academic Rokaya al-Mohareb were freed following the second hearing on Wednesday of their high-profile trial in Riyadh's criminal court, a relative of one of the women told AFP.

The women described undergoing torture during their nine-month detention, sources close to the case told Reuters.

The conditions of their release were unclear and there was no immediate comment from the court.

But the relative said that the women, freed after nearly a year in detention, will still have to appear in court next Wednesday when the trial resumes.

ALQST confirmed the news on Twitter, adding that the other detained women were expected to be released on Sunday.

Most of the women were detained last summer in a crackdown on campaigners just before the historic lifting of a decades-long ban on female motorists.

The women had long campaigned for the right to drive and to abolish the restrictive guardianship system that gives male relatives arbitrary authority over women.