By Tova Cohen

TEL AVIV (Reuters) - Israel is working with authorities in the United States, Britain, France and Belgium to investigate complaints against Israeli firms selling high-risk online options internationally, Israel's chief securities regulator said on Tuesday.

Shmuel Hauser, chairman of the Israel Securities Authority (ISA), said the scale and reach of the online binary options business - short-term bets on the movement of financial instruments- meant closer coordination was required among regulators.

"The United States, England, France and Belgium have asked us for help," he told Reuters on Tuesday. Authorities in those countries were leading their own investigations with assistance from the ISA, he said.

He declined to elaborate on how the investigations were being conducted or which companies were being looked into.

Binary options usually involve betting on whether individual shares, indexes, currencies or other securities will go up or down in a given period of time. The time for the option to "mature" is short - as little as a minute.

Unlike true options, winning bets pay only a fixed return, and they cannot be re-sold. But they can be bought online from a phone or iPad, making them accessible to amateur traders, who can end up losing thousands of dollars in a matter of minutes.

Critics say binary options are just a form of gambling, with the odds often stacked against those making the bets. Many large operators are based in Israel.

Hauser said last month he wanted to expand his authority so he can ban Israeli companies from selling binary options abroad, an acknowledgement that Israel's ban on their domestic sale was not enough to clamp down on the industry [L8N1CX6TO].

He has asked the attorney general to consider amending the law to give him power to target groups that market the options abroad.

Hauser said that currently he can act against firms selling binary options abroad only if international regulators request that he investigate. Normally, he said, the ISA receives around four requests a year from foreign regulators.

"In the last two years, we've had requests for almost 30 investigations, mostly binary options but also some forex companies," Hauser said, referring to online trading platforms for foreign currencies.

A Reuters special report published in September shed light on the extent of the industry and accusations by London-based lawyers who say hundreds of their clients have been duped out of vast sums of money by some Israeli firms.

While the industry markets itself as a legitimate investment, clients of some firms say they are little more than high-pressure scams. They accuse the companies of transferring money between accounts without approval and in some cases of preventing them from withdrawing funds.

Hauser, who estimated the industry was worth hundreds of millions of dollars, possibly more, said he cannot act when an individual complains about a specific company, which is why he is now seeking to have Israel's law changed.

"I don't have the authority, and I think this creates a very bad reputation for Israel. It hurts Israel's integrity," he said.

To try to put the squeeze on the industry, the ISA is working with all enforcement agents in Israel, including the police, Finance Ministry and Justice Ministry, Hauser said.

"I am very disturbed by this phenomenon ... I don't think binary options should be allowed. They hurt the public, especially the weak."

(Reporting by Tova Cohen; editing by Luke Baker, Larry King)