NAGOYA, Japan, April 28 : Japanese parts suppliers to automakers including Toyota face mounting cost and supply uncertainties due to the Iran war, warning that oil-related product price rises could dent profits. Shortages of hard-to-substitute materials such as naphtha-derived products and aluminium could have an outsized impact on production, suppliers said, potentially rippling through manufacturing far beyond their cost base. While vehicle output has so far been maintained, executives at