A top U.S. securities regulator said on Thursday that she was concerned about naked access, where brokers give high-frequency traders unfiltered access to public markets.

I am worried that the proper controls are not being used effectively to make sure that problems aren't created by sponsored (naked) access, Securities and Exchange Commission Commissioner Elisse Walter told Reuters.

Walter is one of five commissioners who make decisions on federal securities rules.

She is the latest policymaker to weigh in on the practice, where traders gain unfettered access to exchanges by renting a brokerage's license. This allows traders to shave precious milliseconds from the time it takes to access markets.

SEC Chairman Mary Schapiro has also voiced concern and said her agency may consider curbs. She has directed her staff to craft rule proposals that would address the risk that naked access poses to exchanges.

(Reporting by Rachelle Younglai, editing by Leslie Gevirtz)