The Geneva-based International Committee of the Red Cross (ICRC) has handed over documents about the Spanish Civil War to the government of Spain.
The archives consist of nearly 80,000 documents, of which 600 are photographs. They include reports on prison visits by ICRC delegates, as well as ICRC and Red Cross correspondence.
The photos show victims of air raids on Madrid, Barcelona and other cities, food distribution and the evacuation of children and the injured.
ICRC President Jakob Kellenberger said he hoped the documents would help Spain "in its efforts to research and preserve the memory of this tragic episode in its history".
The Spanish Civil War lasted from 1936 to 1939 and ended with the victory of the rightwing nationalists under General Francisco Franco.
The Spanish government first asked for copies of the ICRC's archives in 2005 and an agreement was signed in 2006.
The documents will be held in the city of Salamanca, in western Spain.