* Steelmaker raised stake in rival to near 12 pct
* Buying spree came as Techint closed in on deal
SAO PAULO, April 11 (Reuters) - Brazil's antitrust regulator prohibited steelmaker CSN from increasing its stake in rival Usiminas, heading off a stock-buying spree triggered by Italian-Argentine Techint's takeover.
The regulator Cade also suspended shareholder rights associated with CSN's stake, such as naming board members.
CSN raised its holding of Usiminas' common shares to 11.66 percent and its holding of preferred shares to 20.14 percent in November, when Usiminas' controlling group was in talks with Luxembourg-based steelmaker Ternium to sell a minority stake in the company.
Ternium's parent company Techint closed a deal for 27.7 percent of Usiminas that month and tapped a new chief executive to lead a turnaround at Brazil's largest maker of flat steel products.
But CSN continued raising its stake in Usiminas common shares to 11.97 percent by the end of the year and executives said last month that the company would take "all measures possible" to protect the value of its Usiminas stake.