BUENOS AIRES, April 30, 2008 (AFP) - Authorities are 'very concerned' over the disappearance of a second witness to abuses carried out by military dictators in Argentina's 'dirty war,' President Cristina Kirchner said Wednesday.

Juan Puthud, 50, a human rights activist who lost an eye after he was kidnapped and tortured at 18 years of age, was last seen Tuesday night as he was heading to work in Zarate, 90 kilometers (55 miles) north of here, his parents reported to police.

He was a witness in ongoing trials against 'dirty war' offenders. Another witness and torture victim Jorge Julio Lopez, 77, has been missing since September 18, 2007.

Then president Nestor Kirchner -- husband of the current president -- blamed Lopez's disappearance last year on criminals 'linked to state terrorism,' a term used to describe the old military dictatorship that ruled from 1976 to 1983).

Referring to Puthod's disappearance, Cristina Kirchner, in a speech in southern Santa Cruz, said her administration was 'very concerned ... because a key witness in human rights trials has disappeared.'

Buenos Aires Governor Daniel Scioli told reporters an all out effort was underway to locate Puthod, who was in 'fragile health because of his heart and eyes, as a result of the tortures he suffered.'

Officials said some 250 police officers and six helicopters were combing Zarate and its surroundings in search of Puthod, who runs a radio program remembering the dirty war and is a father of four children.

Officials link Lopez's disappearance and possibly Puthod's to intimidation attempts against witnesses in the trials of nearly 1,000 former military and police accused of human rights abuses during the past military regime.

Under the pretext of fighting a so-called 'dirty war' against leftist insurgents, military leaders in Argentina from 1976 to 1983 were responsible for the disappearance of some 30,000 people.