MILAN (Reuters) – The head of Italy’s top retail bank Intesa Sanpaolo (ISP.MI) joined a growing chorus of Bitcoin critics, calling the wild gyrations in the price of the cryptocurrency a speculative bubble and saying global regulatory scrutiny was essential.

“There is no doubt it’s a speculative bubble, when a currency goes from $1,000 to $10,000 in the space of a year the fluctuation is absolutely speculative,” Intesa CEO Carlo Messina told the TG5 news program on Friday.

“The big problem is that there is no regulation,” he said, adding that global financial regulators “must absolutely deal with this.”

Asked whether retail investors should bet their money on Bitcoin, he said: “I would never do it.”

Bitcoin rebounded on Friday to hit the day’s highs above $10,500, recovering from an earlier dip below $9,500, after the U.S. derivatives regulator said it would allow CME Group (CME.O) and CBOE Global Markets (CBOE.O) to list bitcoin futures.

Bitcoin’s rapid ascent has led to countless warnings that it has reached bubble territory. But the warnings have had little effect, with dozens of new crypto-hedge funds entering the market and retail investors piling in.