Saudi Arabia: Saudi authorities have released a prominent human rights lawyer seven months after he was detained in a crackdown on dissent, campaigners said on Monday.

Ibrahim al-Modaimegh, around 80, was released after a "serious deterioration in his health", said Prisoners of Conscience, a Saudi group that tracks political prisoners, in a development corroborated by multiple other activists.

The government has so far not offered any public explanation for his arrest or the conditions of his release.

Modaimegh was among over a dozen activists, including several women, who were arrested in May just before the historic lifting of a decades-long ban on female motorists the following month.

After their arrest, state-backed newspapers published front-page pictures of the jailed activists, including Modaimegh, calling them "traitors".

Modaimegh's release comes as Saudi Arabia faces criticism over the killing of insider-turned-critic Jamal Khashoggi in its Istanbul consulate on October 2.

As for the detained activists, they include Aziza al-Yousef, a retired professor at Riyadh's King Saud University, and Loujain al-Hathloul - who was held in 2014 for more than 70 days for attempting to drive from neighbouring UAE to Saudi Arabia.

Many of the activists are being held without charge or legal representation, campaigners say.

The arrests were seen as a calculated move by powerful Crown Prince Mohammed bin Salman to placate clerics incensed by his modernisation drive, as well as to send a clear signal to activists that he alone is the arbiter of change.

Modaimegh's release "is probably a first step in revisiting many of the arrests of activists carried out" in recent months, said Ali Shihabi, head of the pro-Saudi Arabia Foundation think tank in Washington.

"The untraditional, and very aggressive, approach to the management of dissent... is now being systematically revisited by the (Saudi) leadership," Shihabi said on Twitter.

Government officials did not immediately respond to requests for comment.