A prominent Saudi Imam and preacher at the Prophet's Mosque in Medina has died in prison, reportedly as a result of being held in poor conditions, activists have said.

Sheikh Ahmed al-Amari, former dean of the Quran College in the Islamic University of Madinah, died on Sunday, more than five months after he was arrested, said the social media advocacy group, Prisoners of Conscience, which monitors and documents arrests of Saudi preachers and religious scholars.

The group accused Saudi prison authorities of "intentionally neglecting" the 69-year-old and "causing his death".

#قتلوا_العماري عندما اعتقلوه تعسفياً ..

ثم قتلوه بالعزل الانفرادي 5 أشهر ..

ثم قتلوه بالإهمال الطبي وحرمانه من الدواء والرعاية اللازمة

فأصابه نزيف دماغي ..

تركوه حتى "مات دماغياً" ثم فارق الحياة

كم مرّة قتلوك .. كم مرّة سيلاحق دمُك القتلة !! pic.twitter.com/D1Rlwdy2Yn — معتقلي الرأي (@m3takl) January 20, 2019

Yahya Assiri, director of the London-based ALQST rights group, said al-Amari was arrested from his home in August amid a crackdown that also included the arrest of one of his close associates, Muslim scholar Safar al-Hawali.

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Al-Hawali, 68, was arrested shortly after he published a 3,000-page book which included attacks on Crown Prince Mohammed bin Salman (MBS) and the ruling Saudi royal family over their ties to Israel.

While a number of social media accounts blamed al-Amari's death on medical negligence, Assiri told Middle East Eye (MEE) that the Imam had been held in solitary confinement and "was suddenly transferred from Dhahban prison to the King Abdullah Medical Complex in Jeddah on January 2 after a brain haemorrhage".

"I believe it is a case of murder in custody rather than medical negligence," Assiri told MEE.

Saudi Arabia is yet to issue an official statement on the issue.

The kingdom has faced increased scrutiny since the murder of dissident journalist Jamal Khashoggi inside the Saudi consulate in Istanbul in October.

After offering several contradicting accounts, Saudi Arabia finally admitted that he was killed in a botched rendition operation and his body subsequently dismembered.

Public prosecutors in Saudi Arabia are currently seeking death penalty for Muslim scholar Salman al-Awdah, who had previously called for elections and separation of powers - demands considered dangerous provocations in the kingdom.

Awdah, who UN experts have described as a "reformist," was imprisoned more than a year ago, shortly after MBS launched a crackdown on dissent and imposed a land, sea and air blockade on the kingdom's Gulf neighbour, Qatar.

Saudi Arabia, which bans public protests and political parties, has witnessed a massive crackdown on dissent, with dozens of religious leaders, intellectuals and women's rights activists arrested over the past two years.

Among those arrested are Islamic preachers Awad al-Qarni, Farhan al-Malki and Mostafa Hassan.