There is no evidence that last Thursday's mysterious U.S. stock market meltdown was caused by a cyberattack, a U.S. counterterrorism official said on Sunday.

Asked on the Fox News Sunday program if a cyberattack was behind the nearly 1,000-point drop in the Dow, John Brennan, President Obama's top counterterrorism adviser said: There is no indication that it was.

Brennan said securities regulators were still trying to determine the cause of Thursday's sudden drop in the Dow Jones industrial average.

They are looking at the causes for that ... So they are looking at whatever possibilities that were out there, he said.

The stock slump occurred during rising market concern about the Greek debt crisis and is believed to have been exacerbated by at least one large erroneous trade, labeled by some as a fat finger, or inaccurate key stroke.

Market participants have speculated high-frequency and algorithmic trading magnified the wild swing.

Securities and Exchange Commission officials are considering new curbs to slow stock trades when markets are plunging, two people familiar with the matter told Reuters on Saturday.

(Reporting by Eric Beech; Editing by Jackie Frank)

Cybercrime