Almost 18,000 people have died in Syria's state prisons since the outbreak of civil war in 2011, Amnesty International said today, in a damning report that warned torture is a "routine occurrence" in government detention facilities.

Though state forces have used torture for decades, Amnesty said, "since the current crisis in Syria began in 2011, the situation has become catastrophic, with torture committed on a massive scale".

Researchers interviewed 65 people who were detained between 2011 and 2015. Every one of them said they were tortured or ill-treated during interrogations.

"They had me stand on the barrel, and they tied the rope around my wrists. Then they took away the barrel. There was nothing below my feet. They were dangling in the air. They brought three sticks... [They were] hitting me everywhere," one interviewee said.

"After they were done beating me with the wooden sticks, they took the cigarettes. They were putting them out all over my body. It felt like a knife excavating my body, cutting me apart."

Another said they were beaten until they passed out, and when they woke up their trousers had been opened and undershirt moved up. "Everything was hurting, so I couldn't tell if I has been raped," the victim recalled. "It was overwhelming pain everywhere."

The report, 'It breaks the human': Torture, disease and death in Syria's prisons, said torture is "used routinely to extract false confessions", and is just one of many hardships suffered by inmates. Former detainees reported "appalling" conditions in detention facilities including severe overcrowding of cells, exposure to extreme temperatures, lack of access to medical treatment and being held for days in cells with the bodies of dead prisoners.

Women reported being subjected to sexual harassment and assault, and none were allowed contact with families or lawyers.

According to Amnesty, the Human Rights Data Analysis Group estimates that at least 17,793 people were killed while in custody in Syria between 15 March 2011 and 31 December 2015 – a number that is considered a conservative figure.

"Amnesty International considers that the torture and other ill-treatment of detainees carried out by the Syrian government since 2011 have been perpetrated as part of an attack against the civilian population, pursuant to a state policy, that has been widespread, as well as systematic, and therefore amounts to a crime against humanity," the report said.

"An end to these violations is not yet in sight. The Syrian authorities continue to degrade, arrest, torture, and kill anyone perceived to be opposing them, even in the face of demands from the UN Security Council... This report therefore contains an urgent call on the international community to pressure the Syrian authorities to abide by their international obligations and end the use of torture and other ill-treatment, arbitrary detention and enforced disappearances, and prevent further deaths in custody."