Federal authorities are moving to seize hundreds of millions of dollars in assets in the US tied to the bankrupt cryptocurrency exchange FTX, a sign that the battle over control of the company’s remaining funds is escalating.

Seth Shapiro, a Justice Department official, said at an FTX bankruptcy court hearing on 4 January that the federal government has seized or is in the process of seizing Robinhood shares whose ownership is disputed by FTX and BlockFi, a cryptocurrency lender that collapsed in late November. The Wall Street Journal previously reported that the dispute involves 56 million shares.