Three out of 10 French high-speed trains will be cancelled on Saturday on routes hit by a series of “co-ordinated” arson attacks.

French Prime Minister Gabriel Attal said security forces continued to search for the “saboteurs” responsible after rail networks were paralysed ahead of the opening of the Olympic Games.

National rail company SNCF said services which do run on Saturday will be delayed for up to two hours on major lines running in and out of Paris, while a quarter of Eurostar services will also be cancelled.

France’s transport minister said services would return to normal by Monday morning.

SNCF estimated that about 250,000 passengers were affected on Friday, while junior transport minister Patrice Vergriete said as many as 800,000 could be impacted over three days.

Eurostar – which runs international services from London to Paris and uses a high-speed line in France – said one in four of its trains would not run over the weekend.

Travellers have been advised to postpone their journeys, with disruption expected to last until Monday.

Among Eurostar customers affected on Friday was Prime Minister Sir Keir Starmer, who had planned to travel to the Games’ opening ceremony via train but was forced to fly instead.

He told the BBC: “I’m not going to pretend it wasn’t frustrating because it was, and for very many people it made travel so much harder.”

There has still been no claim of responsibility for the damage, SNCF said.

The company said its staff had “worked all night under difficult conditions in the rain” to repair damage.

The “strategic” vandalism saw cabling boxes at junctions on the North, Brittany and South-West lines set alight hours before the Olympics opening ceremony was due to begin in the capital.

Saboteurs cut and set fire to specialised fibre optic cables essential for the safe functioning of the rail network, government officials said.

A source linked to the investigation told the AFP news agency that the operation was “well-prepared” and organised by “a single structure”.

Rail workers foiled an attempt to destroy safety equipment on a fourth line.

“At this stage, traffic will remain disrupted on Sunday on the North axis and should improve on the Atlantic axis for weekend returns,” a spokesman for the rail network said on Saturday morning.