European Union prosecutors have begun investigating the possible misuse of EU funds meant for upgrading the Spanish railway line where a train crash killed 69 people last week.
Prosecutors backed by a special unit of Spain's Guardia Civil security force said they were conducting the inquiry at the offices of Adif rail infrastructure authority and rail safety agency AESF.
The 28 October accident on the Madrid-Seville high-speed line was one of the worst railway disasters in Europe this century.
It is the second EU fraud inquiry opened into Spain's railways this year, after 46 people were killed on the same line at Adamuz in January.
Last week, a train operated by state-owned operator Renfe ploughed into the back of a stationary train belonging to private Spanish company Iryo outside the village of Urda, around 130km (80 miles) south of Madrid.
The LZB communication system that monitors the position of trains had gone down, and the Renfe train had been given the all clear to start running at normal speed, even though the Iryo train ahead of it had been unable to restart.
The two accidents nine months apart on the same line have claimed 115 lives and dozens more injuries.
The European Public Prosecutor's Office (EPPO) said on Friday it had begun conducting investigative measures at Spain's rail authorities "after the opening of an investigation into possible fraud affecting EU funds allocated to the renovation and upgrading of safety, signalling and communications systems on the Madrid-Seville high-speed railway line".
The EPPO highlighted high public interest in the case, but said no further details would be made public.
As part of the process, a Spanish judge assigned to the case has to ensure the investigation complies with legal safeguards, including authorising any measures that might involve house searches or phone-tapping.
The Urda disaster has damaged the Socialist-led government of Prime Minister Pedro Sánchez ahead of a 29 November general election and the party is trailing the conservative People's Party (PP) in most opinion polls.
Close Sánchez ally Óscar Puente resigned this week as transport minister, after seeing two deadly accidents on his watch this year.
The PP and far-right Vox say Puente's resignation is not enough and they have demanded that Sánchez resign too.
Many people in Spain have now become wary of taking the train, with reports of widespread cancellations and empty station platforms.
A funeral for the 69 victims at Urda will take place on Tuesday at Toledo cathedral, in the same province that the disaster happened.
Puente's successor, Carlos Cuerpo, has vowed to take all necessary measures to "restore the confidence of Spaniards in our high-speed rail".
Cuerpo met survivors of January's Adamuz disaster on Friday and they handed him a list of 11 demands for improving safety on Spain's railways.
