Cryptocurrency exchange Bittrex Inc. (Bittrex) filed for bankruptcy protection on Monday. Three weeks ago, the US Securities and Exchange Commission (SEC) launched a complaint against it for operating an unregistered stock exchange.

Seattle-based Bittrex ceased its U.S. operations on April 30 and said its bankruptcy filing would not affect the business of Bittrex Global, its company that serves clients outside the United States. The company's non-US operations are based in Liechtenstein.

According to its bankruptcy filing with a court in Wilmington, Delaware, Bittrex has assets and liabilities of between $500 million and $1 billion.

Bittrex said it still holds crypto assets of U.S. customers who did not make fund withdrawals before April 30.

These assets are "safe and sound". Bittrex said it intends to ask the bankruptcy court to reopen customer accounts on a limited basis in order to distribute the cryptocurrency back to customers.

Several crypto companies have filed bankruptcy filings over the past year, largely due to falling asset prices and regulatory reviews, with former crypto giant FTX Mired in bankruptcy following criminal charges.

The SEC filed a complaint against Bittrex on April 17, alleging that its former CEO, William Shihara, encouraged issuers of crypto assets offering tokens on the company's platform to remove public statements that could prompt regulators to investigate those token offerings as securities.

Bittrex has denied the SEC's allegations, saying the crypto assets on its platform are not securities or investment contracts.

The SEC's lawsuit is still pending, but Bittrex previously agreed to pay a $29 million fine to the U.S. Treasury Department for "clear violations" of the country's sanctions policies against certain countries and anti-money laundering laws.

Bittrex's petition lists the Office of Foreign Assets Control, an agency of the U.S. Treasury Department, as its largest unsecured creditor, owing more than $24 million to the agency.

Most of Bittrex's other largest creditors are customers of its cryptocurrency exchange. Bittrex listed 16 customers with $1 million or more in their accounts, but did not name them. According to the petition, the client with the most money left had $14.6 million in assets in his account.