RENNES, France, June 14, 2025 (BSS/AFP) - Four people were killed and nine others seriously injured in a motorway accident Friday in western France involving a bus carrying a group of Ukrainian students, authorities said.

Local prosecutors said later Friday that the two Ukrainian drivers had been detained on suspicion of manslaughter and "involuntary wounding".

All four people who died were adults and the bus was the only vehicle involved in the accident, local state official Emmanuel Aubry said.

The group included teenagers aged 15 to 17 travelling back to Ukraine after a school exchange trip, the Ukrainian embassy in France said.

The accident was "very, very sudden", said Ukraine's ambassador to France, Vadym Omelchenko, after speaking with passengers.

"We are in contact with the families of the victims. Some children have managed to reach their parents," said the embassy.

Ukrainian President Volodymyr Zelensky said in a social media post that three of the four killed were Ukrainian citizens.

"Two more people are in critical condition, and French doctors are fighting for their lives," he added, thanking the French authorities for their help for the victims.

French Labour Minister Astrid Panosyan-Bouvet told reporters that 18 other passengers had sustained minor injuries when the bus overturned on the motorway outside the town of Degre, in the Sarthe region, 230 kilometres (140 miles) southwest of Paris.

French Prime Minister Francois Bayrou said he was "thinking of the victims of the terrible bus accident that occurred in Sarthe".

"We will do whatever is necessary to shed light on the circumstances of this accident," he added.