Why were two passenger trains travelling towards each other on the same track?
The question is being asked in Poland after a head-on collision at high speed left at least 15 people dead and dozens injured.
Prime Minister Donald Tusk visited the crash site in a rural area in the south of the country. He described the accident on the Warsaw-Krakow mainline as the most tragic train catastrophe in Poland’s history in many, many years. The premier said it was too early to speculate about what caused it but that human error could not be excluded.
The crash happened near the southern town of Szczechociny at around 9 o’clock local time on Saturday night.
Some 350 passengers were on the trains, including French, Spanish and Ukrainian nationals. More than 50 people were hurt in the crash. Many are said to be in a serious condition.