At least three of the prisoner’s family members have been detained since they published the allegations of sexual assault and torture.
An Egyptian detainee’s allegations of sexual assault and torture by authorities and the subsequent detention of his relatives have sparked widespread outrage and calls for the US to suspend aid to Cairo.
Abdul Rahman Jamal Metwally, widely known as Abdul Rahman al-Shuwaikh, began a hunger strike earlier this month in protest against the alleged abuses.
Shuwaikh was gang-raped by a prisoner and ten prison personnel, his mother said in a Facebook post earlier this month. The reported incident took place on April 6 in the Minya prison.
The 30-year-old was arrested in 2014 following the imprisonment of his father and brother as part of acrackdown on dissent by President Abdel Fattah al-Sisi, who rose to power in a military coup a year earlier.
At least three of Shuwaikh’s relatives were detained earlier this week after the family publicised the sexual assault allegations.
A court ordered his 55-year-old mother detained for a period of at least 15 days while prosecutors investigate allegations that she engaged in “terrorism” and spread “fake news”.
Shuwaikh’s sister was released after four days in detention but the whereabouts of his father remain unknown.
Dozens of American and Egypt intellectuals and civil society figures have called for the United States to halt aid to Egypt in response to the claims.
Signatories of the open letter addressed to President Joe Biden include Noam Chomsky and activists Magda Seikaly, Dina al-Hinnawi and Mona al-Shazly.
Washington gives $1.3 billion in military aid to Cairo every year, making Egypt the largest recipient of US military aid afer Israel. The country receives more than $800 million in additional economic aid.
The letter says that Biden must fulfil his campaign promise to stop writing “blank checks” to Sisi, who former US President Donald Trump described as his “favourite dictator”.
Human rights groups estimate that around 60,000 political prisoners are being held in Egyptian jails.
Thousands of journalists, protesters, activists and civil society figures have been detained since the 2013 coup that ousted democratically elected President Mohammad Morsi.