The newspaper said it learnt the text of the document, which was produced by the Iranian parliament’s Foreign Affairs and Defence Commission, "from Middle Eastern sources".
Stretching to more than 100 pages and published at the beginning of September, the report was the result of six months of work by economic and oil experts, Le Monde said in its edition dated Sunday-Monday.
The report, which reached President Mahmoud Ahmadinejad, said Iran should "make all political efforts to prevent the imposition of sanctions, while preserving the interests of the country and national honour".
If Iran faced heavy sanctions it "would be forced to modify its national priorities and devote most of its resources to prevent a major social upheaval, which could lead to a deterioration in the quality of life for a large section of the population."
According to the text, "the members of the regime who had been heard by the commission indicated that any worsening of the economic situation could cause social troubles that could lead to a deterioration and a weakening of internal stability."
The report’s authors feared the effects of a combined trade embargo on oil heading into and out of Iran.
The report was published — but hardly circulated at all according to Le Monde — nearly three months before the adoption by the UN Security Council of a resolution sanctioning Iran’s nuclear and ballistic weapons programmes because of the enrichment of uranium.
The UN sanctions called for a suspension of all exports of materials and technologies linked to those activities as well as a freeze of assets and restrictions on foreign travel by people tied to the programmes.
The day after the vote, which took place on December 23, Tehran defied the United Nations, saying it was going to start work on installing 3,000 centrifuges to enrich uranium, which can be used for nuclear energy fuel but also to develop atomic weapons.
Washington wanted tougher sanctions against Iran but backed down in the face of opposition from China and Russia.
Iran insists that its nuclear drive is peaceful and solely aimed at generating energy for a growing population.