Ecuador’s tax office SRI is investigating tax declarations of the country’s leading cement producer Cemento Nacional, local paper El Comercio reported.  In 2003, Cementos’ 22 companies between them paid US$13m in corporate taxes, however, 10 companies within the group registered their tax payable as zero, said the paper.  Earlier this month, Cementos announced the sale of five non-core factories to maintain a focus on cement, concrete and aggregate production.  It reported US$240m in net sales and has 62% of the domestic construction market, according to information from its 2003 annual report cited by the paper. Cemento Nacional comprises Agregados Rocafuerte (Agrefort), Hormigones Rocafuerte (Rocafort) and Industrias Rocacem.