The U.S. Department of Justice said Monday that it is seizing and seeking to forfeit $61 million in cryptocurrency allegedly derived from the black-market sale of sanctioned Iranian oil.

The amount represents only a fraction of the operation described by prosecutors in a civil forfeiture complaint. Because the allegations were made in a civil complaint, the forfeiture request remains subject to the court process. According to the filing, a cluster of self-custodied wallets received and distributed more than $1.5 billion in oil proceeds, sending funds to businesses linked to Iran’s Islamic Revolutionary Guard Corps, other cryptocurrency addresses and an Iranian exchange.

The complaint alleges that two China-based companies, Blessed Trust Limited and Hexa Whale Trading Limited, used trading accounts at Binance to launder the proceeds and route them to the Iranian government, its agents and its proxies.

The action comes as the U.S. seeks to restrict Iran’s use of cryptocurrency. In July, the U.S. said it had frozen crypto linked to the Iranian regime, mostly in the form of Tether’s stablecoin. Iran also began a bitcoin-backed insurance service for the country’s shipping companies earlier this year.

Monday’s claim did not specifically mention bitcoin. However, the Iranian government has also used bitcoin to circumvent sanctions. Bitcoin has no issuer and therefore no blacklist function, while bitcoin held without intermediaries cannot be frozen.

“The Government of Iran relies on black-market sales of sanctioned crude oil to fund its military and foster terrorism in the Middle East and around the world, along with other malign efforts to develop a nuclear program and ballistic missiles capable of delivering nuclear payloads,” Deputy U.S. Attorney Sean S. Buckley said in a statement.

“As alleged in the complaint filed today, the Government of Iran used a network of cryptocurrency actors in China and elsewhere to launder more than $1.5 billion in illicit oil money intended to benefit the Iranian military and the terror-designated IRGC.”

The filing alleges that the illicit oil proceeds were laundered through Blessed Trust Limited and Hexa Whale Trading Limited before being funneled back to Iran’s government, its agents and its proxies, according to federal prosecutors.

The U.S. Treasury Department’s Office of Foreign Assets Control said in July that Iran had been avoiding sanctions by accepting bitcoin payments from ships passing through the Strait of Hormuz. OFAC said at the time that Hormuz Safe, a service developed by Iran’s Ministry of Economy, “accepts payment in bitcoin and other digital assets” to bypass sanctions.

The Financial Times reported last week that Iran was using bitcoin to settle cross-border transactions through Iranian cryptocurrency exchanges after the country’s central bank advised citizens to do whatever was necessary to support the economy.

The article was written by Mathew Di Salvo for Bitcoin Magazine.