Attackers set fire on Thursday to the offices of a Salvadoran non-profit group tasked with tracking down children who disappeared during the country's civil war.
Officials from the Probusqueda Association for Missing Children in San Salvador said the premises were torched by three armed, masked men.
"They set fire to rooms which housed the archives, court documents and administrative papers," group spokesman Felix Melendez told AFP.
Melendez said, however, that most of the documents had been backed up as computer files and could be reproduced.
Probusqueda is dedicated to investigating the disappearances of hundreds of children who went missing during the 1980-1992 civil war.
The group, which has located 387 children who disappeared during the conflict, is trying to determine the fates of another 520.
Founded in 1994, it has also taken legal action against former government and military officials accused of abducting the children of leftists opposed to the former military regime.
The children, whose parents in many cases were killed during the conflict, were sometimes sent out of the country for adoption.
Last week, Probusqueda reunited the latest of many cases of separated relatives, when it arranged a meeting between Marina Rivera, now 35, and her biological family.
Abducted in May 1982, Rivera was found to have been adopted by an American family residing in Hawaii.
The civil war in El Salvador, pitting leftist guerrillas against the military junta, killed more than 75,000 people and led to the disappearances of some 7,000.