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Prison guards at a maximum-security jail in the Egyptian capital routinely abuse political prisoners by cramming them into packed cells, and isolating them from their families, lawyers, and doctors, Human Rights Watch said on Wednesday.

In a on Cairo's infamous "Scorpion" Prison looked into the cases of several high-profile political prisoners.

The US-based watchdog described the detainees living in dire conditions with bare cells without beds, and prisoners without soap.

Detainees in Scorpion Prison complex are held behind a "wall of secrecy" by the interior ministry with almost no oversight of wardens actions.

The unit, a wing of the Tora prison complex, holds about 1,000 prisoners, including most of the Muslim Brotherhood's top leadership.

It also includes alleged members of the Islamic State group and various critics of the government of President Abdel Fattah al-Sisi.

"[The prison] sits at the end of the state's repressive pipeline, ensuring that political opponents are left with no voice and no hope," said Joe Stork, the group's deputy Middle East and North Africa director.

"Its purpose seems to be little more than a place to throw government critics and forget them," he added.

	Activists say that police under Sisi are acting with near total impunity [Getty]

The report documents "cruel and inhuman" treatment via interviews with 20 relatives of inmates held in the prison. It asserts the ill-treatment "probably amounts to torture in some cases and violates basic international norms for the treatment of prisoners".

Among those mentioned were Khairat al-Shater, the former deputy head of the now-banned Muslim Brotherhood, as well as onetime Brotherhood lawmaker Mohammad al-Beltagy, former MPs and aides to former President Mohammed Morsi.

The Muslims Brotherhood government was overthrown by the army in 2013.

Authorities then launched a wide-ranging crackdown on dissent with thousands jailed, mainly Sisi's Islamist supporters but also a number of well-known secular activists, and NGO workers.

This month, °®Âþµº obtained a copy of a letter smuggled out of the notorious prison, in which a detainee described the daily conditions of the inmates' incarceration there.

"I was placed in a solitary confinement cell five days after being first questioned. The interrogators deprived me of sleep after days of various torture. When it seemed I was nearly going to die, they put me in the cell," the letter, signed by pseudonym "Ayash al-Assir" ("Ayash the Captive") said.

Activists say that police under Sisi are acting with near total impunity, torturing suspects, abusing detainees and making random arrests.

Authorities are also targeting groups that raise the matter with criminal charges, closure and arrests.