Investigators are looking at all possible causes of the crash, a senior aide to the prime minister said Wednesday.
Renfe's spokesman said he did not know how many crew members were aboard the train when it crashed. Normally, there would be at least five crew members on a train like that, he said.
Officials appealed for blood donations just after the crash but on Thursday said the short-term needs were met.
Herman Van Rompuy, president of the European Council, expressed condolences from the European Union.
Pope Francis, who is on a visit to Brazil for World Youth Day, sent a telegram to the bishop of Santiago de Compostela, Julian Barrio Barrio, offering his support and prayers for all those affected by the tragedy.