Prisoners are badly beaten, not allowed access to toilets, potable water or given enough food, Egypt’s state body for human rights has said after visiting one of the country’s oldest prisons.

A committee of the National Council for Human Rights (NCHR) examined on Monday the prison of Abu Zaabal on the outskirts of Cairo where it met five prisoners.

The NCHR sent the report on the visit to the general prosecutor for investigation.

Monday's visit came in response to a complaint filed by jailed journalist Ahmed Gamal Ziyada, who claimed he was tortured, Salah Sallam, a member of the NCHR said.

Ziyada, who works for the Yaqin network, had leaked, through visitors of a fellow prisoner, a letter detailing abuses against inmates.

"The prison administration has interrogated the assaulted (prisoners) who filed complaints, asking them if they were abused. What do you expect the answer to be after beating, oppression and threats?" Ziyada - who was deprived of visits - wrote in the leaked letter.

Speaking on private channel CBC Extra, Sallam said they had asked authorities to meet with 12 prisoners, all in the jail ward with Ziyada, but they were only allowed access to five. 

Sallam said the group the delegation met were all students in their late teens or early twenties. He said the prisoners, whom he described as frightened, told NCHR they “were threatened with more violence and torture if they speak out about their treatment [by prison authorities]."

The prisoners said they were punished with solitary confinement after the prison authorities found a mobile phone in one cell.

They claimed they were locked up from one week to 16 days in a tiny area of 70 x 150cm.

He said the group in that ward were all students, arrested on accusations of illegal protesting and riots on campus, except for Ziyada.

"We have asked each and every one of them if they were members of the Brotherhood, and they denied it," he said.

While in those cells, prisoners said they were not allowed toilets but rather had to use the tight space they were in, and were only allowed one meal per day: a loaf of bread and cheese.

Prison authorities refused to allow NCHR to examine the alleged solitary confinement cell, Sallam said.

Some of the prisoners claimed that prior to the NCHR's visit jail officials transferred a group of co-inmates, who were seriously wounded [also due to alleged torture], to other facilities.

In one case, Sallam, who is also a doctor, said one prisoner he interviewed showed marks of severe beating with batons on his back.

Some of those NCHR asked to interview have spent 18 months in preventative detention, pending investigation or trials, said Sallam.

“What if after all this period the prisoner turns out to be innocent? Who will compensate him for all those years?”

Calling in to the CBC Extra studio, Abou-Bakr Abdel-Kerim, the interior minister’s aide for human rights, said he “rejected all the claims [of torture]”, maintaining that any allegations could be investigated and verified by the general prosecution.

Abdel-Kerim said prison doctors informed the ministry that the marks on Ziyada’s back were not "a result of baton lashes" but were actually a “birthmark.”

“If there was something going wrong [at the prison], we would have rejected the visit,” Abdel-Kerim said.

“We do not cover up for anyone’s mistakes.”

Allegations of torture in detention cells and during interrogation processes have prevailed in jails and prison stations since the era of ousted president Hosni Mubarak.

The heavy-handedness and brutality of police was one of the main causes that sparked the revolution against Mubarak and his regime in 2011.

After the ouster of Islamist president Mohamed Morsi in 2013 and the subsequent clampdown on his supporters, another wave of torture claims, followed by outcries from human rights groups, surfaced.

The NCHR had paid several visits to different prisons to investigate reports of abuse, and visited a number of prisoners who went on hunger strikes to protest alleged mistreatment, bad living conditions or illegal detention.

A protest law, primarily issued in 2013 to bring back stability to the turbulent streets, jailed thousands of supporters of Mohamed Morsi, non-Islamist government opponents, and students demonstrating on their campuses.

The interior ministry has repeatedly denied all torture allegations.

Egypt's constitution outlaws torture in all its forms, designating it as a crime which carries no statute of limitations.