(AFP) - Greek Prime Minister Kyriakos Mitsotakis on Monday asked the country's Supreme Court to prioritise any criminal cases over last week's deadly train crash and to shed light on what led to the country's worst rail disaster.

"The Greek people want an immediate and thorough clarification of the criminal incidents related to this tragic accident," Mitsotakis wrote in a letter to the court prosecutor about last week's collision, which killed at least 57 people and triggered widespread public anger.

"I ask you to give priority to these cases and, if you deem it appropriate, dedicate an investigation at the highest possible level into what happened" and whether "systemic errors in the rail sector" constituted criminal offences.

With the government seeking re-election in April, the move is seen as necessary for Mitsotakis to placate outrage as such probes in Greece can usually take several years.

The crash occurred in central Greece on Tuesday, when a freight train collided head-on with a passenger train carrying over 350 passengers, many of them young students.

It triggered furious mass protests in parts of the country and clashes with police. Some 12,000 people demonstrated just in Athens on Sunday.

EU Commission President Ursula von der Leyen on Monday tweeted she had discussed providing "further technical support" on modernising Greek railways.

Experts from the commission and the EU Agency for Railways (ERA) will travel this week to Athens, she added after a call with Mitsotakis.

A commission spokesman on Thursday said the EU had already backed 16 railway projects in Greece since 2014 with nearly 700 million euros ($741 million).

The authorities initially blamed the accident on a "human error" by the station master on duty at the time of the collision.

But rail unions say they repeatedly warned operator Hellenic Train about safety issues on the line, and said successive governments' mismanagement of the network and failure to pursue safety reforms had contributed to the fatal collision.

Greek television has showed harrowing images of weeping parents clamouring for information of children who had been aboard the train and berating authorities for what had happened.

Train services in Greece have been curtailed for a sixth straight day.

- Forgiveness -

On Sunday, Mitsotakis asked forgiveness from the families of those killed.

On Friday, he ordered the creation of an expert inquiry to investigate systemic failings in the train system.

Mitsotakis's letter on Monday specified that any investigation by the Supreme Court would be distinct from the experts' inquiry.

He acknowledged that the problems plaguing the infrastructure included delays in technology updates.

"We all know the country's railways are deeply problematic," he said.

For decades, Greece's 2,552-kilometre (1,585-mile) rail network has been plagued by mismanagement, poor maintenance and obsolete equipment.

Safety systems on the line are still not fully automated, five years after the state-owned Greek rail traffic services operator TrainOSE was privatised and sold to Italy's Ferrovie dello Stato Italiane, becoming Hellenic Train.

The stationmaster on duty during the collision, identified as 59-year-old Vassilis Samaras, has admitted being partially responsible for the crash.

He has been charged with negligent homicide and faces life in jail if convicted.

Greek media have reported that the station master was left unsupervised in his post during a busy holiday weekend despite having little experience.

© Agence France-Presse