A former Nazi and fugitive child abuser, Paul Schaefer, has been taken to hospital in Argentina, a day after his arrest ended eight years in hiding.
An Interpol official in Buenos Aires confirmed that Mr Schaefer had been taken ill, but gave no other details.
Schaefer, 83, was a corporal in the German army during World War II.
He set up a religious and farming commune in Chile in 1961, known as Colonia Dignidad, and is now wanted in Chile on child abuse charges.
Schaefer was arrested on Thursday after a joint operation between Argentine and Chilean police ending eight years on the run.
He was taken to hospital 30km (20 miles) outside Buenos Aires suffering from suspected hyptertension, the Chilean news agency Telam reported hospital sources as saying.
Convictions Chile’s most wanted man has long-standing health problems. He suffers from kidney complaints and is confined to a wheelchair.
His Colonia Dignidad community was cut off from the outside world and was believed to have served as an interrogation and torture centre for political prisoners during the military regime of Gen Augusto Pinochet.
The Chilean government has praised the Argentine police for the arrest of Schaefer, and has said he should face a Chilean court as soon as possible.
A Chilean judge late last year convicted and sentenced him in absentia for sexually abusing 26 minors following allegations from victims.
A government spokesman said he was also wanted in connection with the disappearance of a person.
For years, Colonia Dignidad was a mysterious community that was cut off from the outside world by barbed wire fences.
But in recent years former residents have testified of sexual abuse, the use of drugs and the separation of families.
German was the dominant language and Schaefer was the supreme ruler, they said.
The Chilean government says it is waiting for the Argentine government to decide whether to expel him or whether he will need to be formally extradited back to Chile.
Colonia Dignidad still exists and has about 280 residents.
Members have denied they participated in torture but said they had friendly relations with the military, with whom they shared anti-communist philosophies.