It's time for market regulators to clear the air on high-frequency trading, a top Big Board executive said.

NYSE Euronext's chief operating officer waded into the debate over rapid-fire, electronic trading with a call on Monday for regulators to say definitively whether there are problems -- and put a stop to the controversy.

Vilifying high-frequency trading because we don't like that the market is going down, because there's a lot of economic uncertainty, doesn't make a lot of sense, Lawrence Leibowitz told a conference in New York hosted by Barclays.

To be honest, to my knowledge there's been no proof shown that high-frequency trading has been detrimental. So it's sort of unclear why there's this huge cloud, he said.

U.S. and European regulators have warned for at least two years that they could slap new restrictions on hedge funds, banks and proprietary firms that use high-frequency trading (HFT) to send high order volumes and execute short-term trades to make markets or capitalize on price imbalances.

The May 2010 flash crash amplified calls from some investors and politicians for a crackdown, though a regulator report said HFT did not spark the crash. HFT was in the crosshairs again in August when markets globally sold off, punctuated by swift and volatile swings.

While European Union regulators said this summer that HFT raised risks and needs addressing, Reuters reported this month that U.S. regulators have taken the unprecedented step of asking some HFT firms for their secret trading codes.

Leibowitz said it was time for some answers.

I think what it really takes is for the regulators to actually make a statement that says we've looked at this, we've taken everybody's concerns into account, we actually looked at the numbers, and either we don't see a problem, so everyone should stop waving their hands; second, we saw a problem with participants and we are disciplining them; or third, we think there are problems and we're going to do some regulation.

But the ominous silence of the regulators allows the fanning of the flames ... and it's really not clear whether they're based in fact in any way.

Among the moves meant to shed more light on HFT, the U.S. Securities and Exchange Commission in July adopted a large trader rule that will reveal more operating information on HFT, including some detail on the firms' strategies.

HFT is estimated to be involved in more than half of U.S. equity trading volume, and therefore a big chunk of transaction revenue for exchanges like the New York Stock Exchange.

(Reporting by Jonathan Spicer; editing by John Wallace)