U.S. securities regulators are looking into the events surrounding Knight Capital Group's trading glitch this week, which roiled markets and wiped out $440 million of the firm's capital.

"We continue to closely review the events surrounding yesterday's trading and discuss those events with other regulators as well as Knight Capital Group," Securities and Exchange Commission spokesman John Nester said.

"We also are considering what, if any, additional steps may be necessary, beyond the post-Flash Crash measures that limited the impact of yesterday's trading."