The US Department of Justice and embattled mayor Rahm Emanuel are under mounting pressure to investigate allegations of what one politician called “CIA or Gestapo tactics” at a secretive Chicago police facility exposed by the Guardian.

Politicians and civil-rights groups across the US expressed shock upon hearing descriptions of off-the-books interrogation at Homan Square, the Chicago warehouse that multiple lawyers and one shackled-up protester likened to a US counter-terrorist black site in a Guardian investigation published this week.