May 21 (Reuters) - The U.S. securities regulator on Monday asked Nasdaq and CBOE to fine-tune their applications to list spot ether exchange-traded-funds (ETFs), signaling the agency may be poised to approve the filings, three people familiar with the process told Reuters.

While the exchange applications are the first step in a two-step approval process, a Securities and Exchange Commission green light would mark a major -- surprise -- win for the cryptocurrency industry that had been expecting the thumbs-down.

The price of ether jumped as much as 18% Monday, and was up another 2.5% at $3,764 early Tuesday morning.

The SEC must decide whether to approve applications filed by CBOE to list ether ETFs provided by VanEck and ARK Investments/21Shares by the end of this week. The SEC had not engaged with exchanges and issuers on the filing details, leading industry executives to expect a thumbs-down.

But in a surprise move, SEC officials on Monday asked Nasdaq and CBOE to quickly make updates and changes to the filings, requests which usually precede approval, said the people who declined to be identified discussing private regulatory matters.

Spokespeople for the SEC and CBOE declined to comment. Spokespeople for Nasdaq and ARK did not return a request for comment.

Reuters could not immediately verify if NYSE Arca, the third exchange involved, had also been contacted by the SEC.

The exchange applications seek SEC approval for a rule change required to list new products, but the issuers still need the agency to approve the ETF registration statements before they can start trading.

Unlike the exchange filings, there is no set time frame in which the SEC has to decide, meaning it could still take several months for ether ETFs to being trading. (Reporting by Suzanne McGee and Hannah Lang in New York; Editing by Chizu Nomiyama)