JOHANNESBURG (AP) — South African police are investigating a possible international gold smuggling syndicate after three suspects were arrested at O.R. Tambo International Airport in Johannesburg with gold bars weighing 73.5 kilograms (162 pounds) in their carry-on luggage.

The gold bullion, worth an estimated $4.1 million, looked suspicious when the three put their bags through a security check, according to the police.

“Upon questioning of the suspects and further inspection of their hand luggage, officials discovered the gold bars and some foreign currency,” said police spokeswoman Col. Athlenda Mathe.

The suspects provided police with certification papers for the gold and South African authorities will work with Interpol and the countries involved to verify the origin and destination of the gold bars, she said.

“There is a possibility that money laundering and fraud charges will be brought against the three accused at a later stage,” said Mathe.

The three Madagascar nationals, who were traveling from Madagascar to Dubai in the United Arab Emirates via South Africa and Ethiopia, made their first court appearance Monday and are due back in court for a formal bail application on Jan. 12.