As France marks the 60th anniversary of the death of Albert Camus on Saturday, a previously unpublished letter written by the Nobel prize winning-author during the Nazi occupation, expressing his anguish and uncertainty for the future of the country, has emerged.

In the missive, found in the archives of France’s wartime leader Gen Charles de Gaulle, Camus detailed his fears that the mass killing of so many able-bodied compatriots was also destroying the “lively and vibrant ideas” that would guarantee his country’s future.

The three-page typed document was written in 1943 when France was under the yoke of the collaborationist Vichy regime of Marshal Philippe Pétain and the Nazis.

The author of La Peste (The Plague) and L’Étranger (The Outsider), then aged 30, had been secretly approached by the “Information Commissariat” of the Committee of National Liberation – based in Algiers – along with other journalists, writers and thinkers, trapped in occupied France.

French forces outside the country were trying to gauge the mood inside.

The document, headed “From an intellectual resistant”, begins: “Here I very briefly summarise the feelings of a French intellectual in the face of the current situation as it can be observed from within the territory. To put it plainly, his first feeling would be one of anguish. My deep conviction is that the form of war that metropolitan France has adopted and in which we are all engaged, can lead both to the rebirth of this people and to its definitive fall.”

The philosophical treatise insists that the French were not discouraged, but in turmoil: “And this double feeling of anguish and uncertainty defines the climate in which most French people live. It would be childish to believe that this leads at the same time to discouragement. Quite precisely the opposite is true, but once again those who have taken charge of the country’s external destiny should not ignore the turmoil that accompanies most minds here.”

Camus’ greatest concern seems to be the renewal of the country’s intellectual elite following the widespread “appalling destruction” of thinkers. This, he insisted, is a “pressing call … vital for the future of France”.

“Justice and freedom cannot be mutually exclusive and are still essential for rebuilding the world and opposing the destructive logics of history,” he wrote.

“The systematic waste of able-bodied individuals in the county is not only killing the country but also the lively and vibrant ideas that will ensure its future. This is what we must avoid and it’s this situation that we must remind people of every day, every hour if necessary in all articles, all broadcasts, all gatherings, all proclamations aimed at those who set the pace of this war. The rest is up to us.”

Camus died on 4 January 1960 when the car he was travelling in driven by his publisher Michel Gallimard crashed into a tree. The author, aged 46, was killed instantly; Gallimard died a few days later.

In a recent book, Italian author Giovanni Catelli claimed Camus was assassinated by KGB spies in retaliation for his anti-Soviet rhetoric.

Camus had sided publicly with the Hungarian uprising from the autumn of 1956, and was highly critical of Soviet actions. He also openly praised and supported the Russian author Boris Pasternak, who was seen as anti-Soviet.

Historians, who have long thought to have discovered everything the Algerian-born Camus wrote, said the wartime letter was a rare find.

The full text is to be published in a new book about Camus by Vincent Duclert, historian and professor at the elite Sciences Po.

Camus: Des Pays de Liberté (Camus: Countries of Freedom) is published on 9 January.