A prominent Saudi cleric arrested in a crackdown on dissent has since been held for four months without charge or contact with the outside world, Human Rights Watch said Sunday.
Salman al-Awda was among more than 20 people arrested in September in what the Saudi government has said was a crackdown on "intelligence activities... for the benefit of foreign parties against the security of the kingdom and its interests."
Awda's family, however, believes he is being held over a tweet linked to neighbouring Qatar, with which Saudi Arabia has cut all ties over accusations of links to Iran and Islamist extremists, according to HRW.
Awda has been held since then in solitary confinement and has been neither charged nor interrogated, said the New York-based watchdog.
The cleric has reportedly been allowed one phone call, in October.
Saudi activists have said Salman al-Awda's brother Khaled has also been detained for disclosing that the cleric had been arrested.
Dozens of Saudi citizens have been convicted on charges linked to dissent and under the country's sweeping cybercrime law, particularly linked to posts on Twitter.