The Syrian regime inflicts at least 72 kinds of torture on prisoners in its detention facilities, according a report that estimates the methods that have resulted in the deaths of at least 185 people this year and more than 14,000 over the course of the civil war.

The forms of torture documented in the report range from scalding with boiling hot water and slicing off body parts to rape and other sexual violence, and medical neglect including allowing junior doctors to use prisoners for surgical training.

Another practice involves leaving detainees who are slipping into delirium in cells with healthier captives. Several torture survivors told the Syrian Network for Human Rights (SNHR), which produced the report, that sharing a cell with such prisoners – who would often be hallucinating or crying hysterically – was “worse than the physical torture inflicted on them by the Syrian regime”.

The organisation established the torture methods from interviews with survivors and witnesses and estimated the death toll partly by examining more than 6,000 pictures of murdered Syrians exposed by a former regime photographer known by the alias “Caesar”.

It noted that Caesar’s photos, which were smuggled from Syria on thumb drives hidden in his shoes, and the interviews gave only a glimpse of the true number of torture methods employed by the regime, which it said, like the death toll, was “likely to be far higher”.

One witness account claimed prison officers used the back of a grenade to smash the teeth of a detained 15-year-old boy. “One one occasion they sprayed insecticide all over [the boy’s] body, set him on fire then wrapped his body with gauze, and from time to time they peeled the gauze [and] lifted his skin with a blade,” says the witness, himself a torture survivor.

The Syrian government has consistently denied allegations that it systematically tortures prisoners. The regime ratified the international convention against torture in 2004 as part of a wave of purported liberalisation enacted by the president, Bashar al-Assad, in the early years of his tenure.

The SNHR also documented 57 deaths from torture at the hands of extremist Islamist groups, 43 caused by the armed opposition to the Assad regime and 47 by the US-backed Syrian Democratic Forces.

It said 14,131 people had been tortured to death so far by the government. “No month in all the years since 2011 has passed without us documenting dozens of deaths due to torture in the Syrian regime’s centres, which is still continuing to the current date,” it said.

About 1.2 million Syrians, or one in 18 of the population, are estimated to have been arrested or detained at some point in the country’s nearly nine-year-old civil war. At least 127,000 people are presumed to either be dead or still in custody, according to an SNHR database.

The existence of Caesar’s cache of more than 55,000 photographs was revealed by the Guardian in January 2014. The former military police photographer documented the killings of about 11,000 detainees before he defected and fled the country.

His images, taken between March 2011 and August 2013, shocked the world and are regarded as crucial possible evidence for any future war crimes proceedings against Assad regime officials.

Groups including the Commission for International Justice and Accountability (CIJA), a US- and EU-funded NGO, have been working for years to collect and store evidence that may be used in future international court proceedings against Syrian officials.

Last year international arrest warrants were issued for Ali Mamlouk, a former national security head, and Jamil Hassan, a former leader of the Air Force Intelligence Directorate.

German police arrested two former Syrian secret service officers in February on suspicion of involvement in torture and crimes against humanity, the first time western criminal prosecutors have arrested alleged torturers working for Assad.