The letter also urges the Saudi authorities to clarify Al-Muraisy’s current situation. His family has not seen him or heard from him since he was arrested at his home on 1 June. They do not know why he was arrested or where he is being held.

Local human rights groups say Al-Muraisy is very popular and influential online and has more than 100,000 Twitter followers. His arrest may have prompted by a few critical tweets and his links with activists, intellectuals and journalists who have been held since last year.

At least 11 journalists and citizen-journalists are officially imprisoned in Saudi Arabia, while around 15 other professional and non-professional journalists are being held without any official confirmation. Saudi Arabia is ranked 169th out of 180 countries in RSF's 2018 World Press Freedom Index.

Signed by ALQST for Human Rights in Saudi Arabia, the Gulf Centre for Human Rights, PEN International, English PEN, Index on Censorship and RSF, the joint letter can be read in both Arabic and English language versions here.