(c) where the importer or the exporter has produced all the necessary documents and furnished full information for the assessment of duty but the proper officer deems it necessary to make further enquiry for assessing the duty; the proper officer may direct that the duty leviable on such goods may, pending the production of such documents or furnishing of such information or completion of such test or enquiry, be assessed pro- visionally if the importer or the exporter, as the case may be, furnishes such security as the proper officer deems fit for the pay- ment of the deficiency, if any, between the duty finally assessed and the duty provisionally assessed.