SAO PAULO, July 13 (Reuters) - Executives of Brazilian steelmaker CSN on Wednesday questioned the business relationship between controlling shareholders of steel rival Usiminas, in which CSN is a minority shareholder.

In the latest chapter of an ongoing shareholder battle, lawyers and executives for CSN told a media briefing in Sao Paulo that they believed there was evidence of collusion between controlling shareholders Nippon Steel & Sumitomo Metal Corp and Techint, resulting in massive losses at Usiminas.

(Reporting by Guillermo Parra-Bernal; Editing by Chizu Nomiyama)