U.S. regulators have worked around-the-clock for the past week as they sort through the collapse of futures brokerage MF Global Holdings Ltd securities regulator Mary Schapiro said on Thursday.

We have struggled with the issues with respect to MF Global, and our teams have worked really hand-in-hand as we sort through the issues there on a virtually 24-hours-a-day basis for the last week, Schapiro, chairman of the U.S. Securities and Exchange Commission, said during a financial fraud conference held by the Financial Industry Regulatory Authority.

The SEC and FINRA are among MF Global's regulators.

MF Global filed for bankruptcy protection on Monday, after risky trades on European debt triggered its collapse. Regulators are attempting to account for a roughly $600 million shortfall in customer funds.

(Reporting by Sarah N. Lynch, editing by Gerald E. McCormick)