Abdel-Hakim Al-Dakhil, son of former Saudi Deputy Minister of Finance Abdulaziz Al-Dakhil, revealed that his father is currently being detained at Al-Ha'ir Prison, south of Riyadh.
Al-Dakhil was detained last Ramadan, along with two others, for paying tribute to reformist Abdullah Al-Hamid, who recently died in prison.
Al-Dakhil's son announced in a widely-circulated video that his father was detained at Al-Ha'ir Prison, and that the reason for his arrest was a tweet calling for freedom and justice.
He called on the families of the detainees to reveal the names of their imprisoned sons and daughters and the violations they are subjected to, in support of the efforts of the Prisoners of Conscience to end injustices and achieve dignity.
The Prisoners of Conscience, an organisation concerned with the affairs of detainees in the Saudi Kingdom, confirmed on their Twitter account the arrests of three writers and activists, namely: Aqel Al-Baheli, Abdulaziz Al-Dakhil and lawyer Sultan Al-Ajmi.
READ: Saudi Arabia considers asset sale and income tax to boost economy
The account referred to tributes written by the detainees on social media platforms, grieving Al-Hamid, who is described as a "leader of Saudi jurists and reformists".
The three detainees extended their condolences to Al-Hamid's family, and talked about his qualities, while one of them indicated that he had spoken to the late activist over the phone days before his death.
Al-Hamid died in his prison cell on 24 April, on the first day of Ramadan, due to what Saudi human rights organisations described as "deliberate medical neglect".
The 70-year-old activist had suffered a stroke and went into a coma, as the authorities refused to release him despite his age.
Al-Hamid was one of the most prominent advocates of reform in the kingdom, and one of the founders of the HASEM project (Saudi Civil and Political Rights Association).
He was arrested several times during his career, the last of which was in March 2013, when he was sentenced to 11 years in prison.
READ: Saudi King Salman chairs cabinet meeting from hospital