Cabral, 74, had been in Guatemala for a concert series, the Buenos Aires Herald reported. He was being driven to the airport with his agent about 5:30 a.m. when their sport utility vehicle was attacked.
Interior Minister Carlos Menocal said Henry Farina, a Guatemalan businessman and promoter who had arranged Cabral's concerts, appeared to be the target and not the singer, La Prensa Libre reported. Farina was driving the car and was wounded in the attack.
Menocal said the ambush, involving three vehicles, appeared to be the work of organized criminals.
A police spokesman said Cabral's agent was hospitalized and was reported to be in stable condition, CNN said.
Cabral, first known in Argentina as a protest singer, was named a UNESCO "World Peace Messenger" in 1996. His best-known song, "No Soy De Aqui, Ni Soy De Alla" or "I'm Not From Here Nor There," has been covered by many Hispanic singers and by Neil Diamond.