Human Rights Watch issued Tuesday a report describing an archipelago of torture chambers in Syria's overcrowded prisons where the Assad regime perpetrates beatings, electrocutions, pulling out toenails and hanging in stress positions on its opponents.

The allegations have been derived from interviews with more than 200 former prisoners and security officers who have fled the war-torn country. More than a dozen Syrians interviewed independently by CNN corroborated the claims.

The guards hung me by my wrists from the ceiling for eight days, one man, identified as Elias, told the organization. After a few days of hanging, being denied sleep, it felt like my brain stopped working.

The report identified four state security agencies, which are collectively referred to in Arabic as al mukhabarat (meaning literally the intelligence), as playing instrumental roles in the systematic torture of perceived enemies of the state.

To manage the thousands of people detained in the context of anti-government demonstrations, the authorities also established numerous temporary unofficial holding centers in places such as stadiums, military bases, schools, and hospitals where the authorities rounded up and held people during massive detention campaigns before transporting them to branches of the intelligence agencies, said the report.

Human Rights Watch says the people interviewed identified 27 clandestine torture centers in Damascus, Daraa, Homs, Latakia, Idib and Aleppo.

The Syrian government denies any allegations of human rights abuses.

British Foreign Secretary William Hague said the report exposes the injustices taking place in the country's civil war. Russia backs the Syrian government, which has spent billions buying war technology from Moscow over the years.

Western allies were forced by Russia's resolve to accept the possibility of Assad's Ba'athist government playing a role in any transitional government during a summit in Geneva on Saturday - a move thoroughly rejected by Syria's opposition and the Arab League.

Meanwhile, in an attempt to cool Turkey's anger over the Syrian shooting down of one of its warplanes over what it claims was international waters in the Mediterranean, Assad expressed condolences for the action, claiming his gunners thought the jet was Israeli.