MEXICO CITY (AP)  Refineries in the United States bought millions of dollars worth of oil siphoned from Mexican government pipelines and smuggled across the border  in some cases by drug cartels expanding their reach, the United States Justice Department said on Monday.

At least one American oil executive has pleaded guilty to a conspiracy that involved what prosecutors said was about $2 million in stolen Mexican oil, Justice Department officials said.

On Tuesday, the United States Department of Homeland Security is scheduled to hand over $2.4 million to Mexico’s tax administration, the first batch of money seized during a joint investigation into smuggled oil that the authorities expect to lead to more arrests and seizures.

“The United States is working with the Mexican government on the theft of oil,” said Nancy Herrera, spokeswoman for the United States attorney’s office in Houston. “It’s an ongoing investigation, with one indictment so far.”