Federal authorities announced in Miami on Wednesday the interception of 90 fuel shipments suspected of being part of a scheme to bust U.S. sanctions on Cuba.

The shipments — more than 600,000 gallons of middle distillates mixed with biodiesel, valued at roughly $2.8 million — were seized as part of the investigation. Details were laid out at a press conference led by Homeland Security Investigations Miami’s José R. Figueroa, Customs and Border Protection’s Daniel Alonso of the Miami/Tampa field office, and the Bureau of Industry and Security’s Jeremy Shein.

Neither the suspected Cuban recipient nor the shippers have been publicly identified, according to reports from Diario Las Américas. The investigation is ongoing.

The seizures come weeks after the U.S. Coast Guard boarded the cargo ship Grace in the Caribbean on Sept. 5 while it was en route to Cuba, as Washington steps up enforcement of its Cuba sanctions regime.