The United States and Britain are reviewing more than $20 billion in cryptocurrency transactions through the Russian virtual exchange Garantex to crack down on circumventing sanctions to support the war in Ukraine, Bloomberg reported. People familiar with the matter said the payment transactions under review were conducted through USDT, a cryptocurrency pegged to the U.S. dollar, on Moscow’s Galantex exchange. The deals have been ongoing since Galtex was placed on the sanctions list.

The Biden administration has been trying to clamp down on cryptocurrency exchanges like Gallontex since the early days of the war. People familiar with the matter said the $20 billion deal could be the biggest breach of sanctions against Russia since the war began. They also warned that due to the complexity and opacity of cryptocurrency transactions, the investigation is still ongoing and the outcome of the investigation cannot be predicted at this time. People familiar with the matter said there is currently no indication of any irregularities by Tether Holdings, which is registered in the British Virgin Islands.