Investigations are underway in the United States after the discovery in a rail car of the badly decomposed bodies of as many as 11 people who may have been illegal immigrants from Mexico.

The grim find was made by workers at a grain handling facility near the town of Denison, Iowa.

Local authorities said foul play was not suspected.

A Mexican consul in the region, Jose Luis Cuevas, was quoted by the Associated Press news agency as saying railway officials had given him the impression that the bodies had been in the car for at least four months.

He said the Mexican authorities had been notified and would make enquiries about possible missing nationals.

Locked in?

Workers had apparently been opening up a long line of rail cars which had been in storage for months when they discovered the remains on Monday.

A senior official with the US Immigration and Naturalisation Service for the region said the victims had boarded the train in Mexico, but their nationality was unconfirmed.

Jerry Heinauer said the authorities did not yet know whether the occupants of the rail car were being smuggled.

"Unfortunately it does happen occasionally that smugglers lead migrants into the United States and then they lock them in cars so that authorities wouldn't check the cars", he said.

Crawford County Sheriff Tom Hogan said the bodies were being taken in the rail car to the state capital Des Moines for investigators to examine.