RIO DE JANEIRO • South American fans of Aerosmith have bitter "medicine" to take.

The rock band announced on Tuesday that they are cutting short a tour of that continent after frontman Steven Tyler flew back to the United States due to "unexpected medical issues".

"To everybody in South America - Brazil, Chile, Argentina and Mexico - I'm very sorry and feel like I've let you down," the 69-year-old wrote in a statement posted on Twitter, without specifying the nature of the illness.

"I won't be able to continue the last four shows of this tour.

"I flew back to the US on doctor's orders last night."

"Please not to worry," he continued, "I am not in a life-threatening condition, but I need to deal with this right away and get some rest and medical care immediately to sustain and maintain my future performances.

"As they say: 'We humans make plans and God laughs.'"

The band played on Monday night in Sao Paulo after performing last Thursday in Rio de Janeiro.

The cities cut from the tour are Curitiba, Brazil; Santiago, Chile; Rosario, Argentina; and Monterrey, Mexico.

Aerosmith announced last year that they were doing a "farewell" tour for 2017, but stopped short of saying the shows would be their finale.

The Boston-bred hard rock group formed in 1970 and are behind such classics as Dream On, Walk This Way and Janie's Got A Gun.

AGENCE FRANCE-PRESSE