The U.S. Securities and Exchange Commission has rejected another round of attempts to list exchange-traded funds backed by bitcoin, blocking ETFs from ProShares, GraniteShares and Direxion, on concern prices could be vulnerable to manipulation.

In a trio of orders posted on the agency¡¯s website Wednesday, the commission said proposals to allow the funds failed to show how exchanges seeking to list the products would ¡°prevent fraudulent and manipulative acts and practices.¡±

The SEC had already denied a request to list a bitcoin ETF run by twins Cameron and Tyler Winklevoss in late July, citing a similar rationale. In that case, it wrote that the platform that would have listed their fund failed to prove the underlying market was ¡°resistant to manipulation.¡±

The SEC¡¯s resistance to cryptocurrency ETFs has taken a toll on bitcoin¡¯s price this year. But the earlier ruling had been widely viewed as a bad sign for remaining proposals, sapping some of the surprise from Wednesday¡¯s decisions. After plummeting more than 50 percent this year, the top cryptocurrency rose less than 1 percent in early trading on Thursday in Asia to around $6,360.

¡°The commission emphasizes that its disapproval does not rest on an evaluation of whether bitcoin, or blockchain technology more generally, has utility or value as an innovation or an investment,¡± the regulator wrote Wednesday. Rather, it disapproved because ¡°the exchange has not met its burden.¡±