The French Foreign Legion’s notoriously tough approach to military training is to be examined in a court in Lyon where four officers and junior officers face trial for manslaughter over the death of six recruits who died in an avalanche.

Lawyers have accused the elite force of a “lack of humanity” in pushing soldiers to their limit after an exercise on a mountainside in January 2016 left six dead and seven injured. The group of 52 soldiers came from a southern French unit of the male-only force which is made up of largely foreign recruits.

In the final stages of preparation before being sent to French operations in west Africa, the men were ordered to enter a difficult area of mountainside in Valfréjus, Savoie, with sealskins, skis and rescue equipment. The exposed, uneven mountainside, at an altitude of 2,600 metres (8,530ft), was treacherous and weather conditions were risky.

At about 1pm there was what was described as a terrible cracking sound and a cry of “Avalanche!”. Six soldiers died: an Albanian, a Hungarian, a Nepalese, a Moldovan, an Italian and a Madagascan who had taken French nationality. Seven others were wounded.

The investigation found an expedition on that mountainside required extreme vigilance and knowledge on the ground. The trial, which begins on Thursday, will examine whether the officers failed to consult local mountain experts, gendarmes and weather forecasters.

Jean-Michel Quillardet, a lawyer for a Ukrainian soldier who was injured, said the men were pushed to their limit and continued the mission because they did not want to let their captain down. He noted that the most senior members of the hierarchy were not on the march but instead involved in administrative tasks that day.

“The investigation dossier is very clear: there was a risk of avalanche,” Quillardet told France Inter radio. “First, the soldiers who decided on the exercise didn’t make contact with weather services or ski slope agents to at least inform themselves whether there was a danger or not. Second, during the march [on the mountain], there were witnesses who said they were ‘going through hell’. I will plead that, for these legionnaires, a lot from other countries, it was ‘march or die’. This is a concept of military command that seems absurd in the 21st century: officers lacked humanity.”

A lawyer for the accused officers denied they had been imprudent, arguing that the avalanche was not their fault.

In 2015, four former French Foreign Legion soldiers were given suspended prison sentences for violence against a fellow recruit who died from heatstroke during an exercise in one of the legion’s toughest desert training camps, in Djibouti. In 38C (100.4F) midday heat, the recruit’s water was taken from him, poured out and a soldier ordered that no more should be given to him. Punches followed and eventually, after begging “water, water”, the recruit collapsed. The soldiers were expelled from the force after the incident, which was described by the legion as “monstrous” and “unacceptable”.

The French Foreign Legion — which once conjured up images of white kepis, brutal tests and men on the run from the law, thanks to films such as Beau Geste, starring Gary Cooper — is now a streamlined elite force which is engaged in many of France’s most important military operations.