In an integrated flexible installation for producing ammonia and urea, the improved method which consists in that a portion of the gaseous stream comprising carbon dioxide, hydrogen and nitrogen is fed to a complementary decarbonation area and then admixed with a portion of a similar, but non-decarbonated stream of gas prior to entering the carbon-dioxide-absorption unit. Liquid ammonia is recovered from a portion of the ammoniated aqueous solution used for abating the ammonia and sent to a distillation column to recover liquid ammonia therefrom.