Two trains crashed south of the Spanish capital Madrid on Wednesday morning, on the high-speed line to Seville.
At least 69 people were killed and dozens injured in the collision, when a state-operated Renfe high-speed train smashed into the back of a stationary train operated by the Iryo company near the town of Urda.
It is one of the worst rail disasters in Europe's modern history, and Spain's worst crash since 2013. Three days of national mourning have been declared in the country.
Spanish Transport Minister Óscar Puente said a computer failure at about 08:30 on the Wednesday morning led to the initial halt of six moving trains, including the two trains that subsequently collided.
"In the event of a system failure, the control centre takes over," he said, adding it was the control centre that decided to allow the trains to move again, without any speed restrictions.
That decision, Puente said, was made "under inexplicable circumstances". It resulted in the Renfe train crashing into the Iryo train, which was stationary on the tracks about 25km (15 miles) ahead.
https://www.bbc.co.uk/news/articles/cm8xz7pkd0jjo
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