CHICAGO (AFP) - Officials scrambled on Tuesday to get 18 human heads off to their final destination, a crematorium, after they were seized by US customs inspectors before Christmas at Chicago's main O'Hare airport.

The heads, each tagged with a name plus place and cause of death, had originated in the United States for use at a research facility in Rome, spokesman Mary Paleologos of the Cook County medical examiner's office said.

"The heads were anatomical specimens used for research, properly preserved, wrapped and labelled when they arrived" back on US soil as regular cargo in three sealed containers on a Lufthansa flight for final disposal.

But as the embalmed heads passed through an X-ray machine at O'Hare, one of the busiest airports in the United States, they were confiscated by customs agents who determined the accompanying paperwork was unclear.

"Right now, they're getting the paperwork cleared up" to enable the heads to proceed to their final destination, a cremation service in the Chicago area, Paleologos told AFP.

In the meantime, the heads remain in storage at the Cook County morgue.

Paleologos was unable to identify the research facility in Rome.

The United States, where human remains can be willed to science, is a major centre in a growing international trade in body parts used for medical research.