An executive for the world's largest asset manager said this week that he doesn't see the case for a bitcoin exchange-traded fund (ETF).

Speaking with Bloomberg on October 3, Mark Wiedman, who serves as Global Head of iShares and Index Investments for BlackRock, was asked about his views on the prospects of a cryptocurrency-tied ETF. A number of firms have attempted to launch such a product, but to date the SEC has been largely dismissive of the concept, issuing notable rejections in the public and, in other cases, prompting some bitcoin ETF backers to withdraw their efforts.

Wiedman said in the interview that he doesn't see it happening, citing other ETF-related products that the firm would encourage clients to hold "in perpetuity." In the case of bitcoin, Wiedman said that he "would not encourage a client to hold bitcoin in perpetuity."

On the question of an ETF specifically, Wiedman went on to say:

Wiedman isn't the only BlackRock executive to comment on cryptocurrencies this week.

That same day, BlackRock CEO Larry Fink was quoted as saying that he is a "big believer" in the potential of cryptocurrencies. That said, he took aim at the speculation in the market and suggested that cryptocurrencies are being buoyed by money laundering.

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