A Homeland Security Department internal watchdog says U.S. Immigration and Customs Enforcement could have saved millions of dollars on charter flights carrying deported immigrants to their home countries by not leaving seats empty.

The Inspector General report says ICE Air flights, which mostly returned deported immigrants to Central America, could have saved up to $41.1 million dollars by flying at capacity. According to the report, ICE spent about $116 million on flights from October 2010 through March 2014 that flew at less than 80 percent capacity.

The report acknowledges various factors prevent ICE's aircrafts from flying at full capacity, but recommends the agency determine better data and management plans for its air removal operations to ensure it uses its resources effectively.

ICE officials said the agency would comment later.