( CNN ) -- Two men held in the Netherlands may have been trying to test U.S. airport security by putting bottles with electronic devices attached in checked baggage , a U.S. law enforcement source said Monday . The men were taken into custody after landing in Amsterdam on a flight from Chicago , Illinois , Dutch prosecutors said . Both men were being held at Amsterdam 's Schiphol International Airport at the request of Dutch national police , airport spokesman Robert Kapel said . The U.S. Department of Homeland Security said they were arrested after `` suspicious items '' in their luggage raised concern . `` The items were not deemed to be dangerous in and of themselves , and as we share information with our international partners , Dutch authorities were notified of the suspicious items , '' the U.S. agency said . `` This matter continues to be under investigation . '' Those items were an empty shampoo bottle with watches attached to it and an empty bottle of a stomach medicine with mobile phones attached , according to the U.S. law enforcement source , who has been briefed on the investigation . That has raised concern that the men may have been testing a future terrorist plot , the source said . Attempts to sneak liquid explosives aboard jetliners were at the heart of a 2006 plot broken up by British authorities . That case led U.S. authorities to ban all but small quantities of liquids from aircraft cabins . U.S. law enforcement officials told CNN that the checked bags contained knives and box cutters as well . Passengers have been banned from carrying those items on aircraft since the September 11 , 2001 , attacks on New York and Washington . The source identified the men aboard United Airlines Flight 908 , from Chicago , Illinois , to Amsterdam , as Ahmed Mohamed Nasser al-Soofi and Hezem al-Murisi . Al-Soofi began his trip by boarding a flight in Birmingham , Alabama , and al-Murisi originally flew from Memphis , Tennessee , the law enforcement source said . Another U.S. law enforcement official said both men were in the United States legally , but their countries of origin were not immediately known . That official said neither of the passengers were carrying items that are barred from aircraft , and federal air marshals were aboard the Chicago-to-Amsterdam flight . However , the law enforcement source said al-Soofi was ticketed for a flight that went to Washington 's Dulles International Airport , with continuing stops in Dubai and Yemen , while both he and al-Murisi were aboard the Chicago-to-Amsterdam flight . Al-Soofi 's luggage went aboard the Chicago-to-Washington flight without him , the source said , in what amounted to another violation of U.S. safety protocols . A U.S. government official said items in at least one of the bags were being examined by law enforcement authorities at Dulles on Monday night . The official said al-Soofi and al-Murisi were seated near each other on the Chicago-to-Amsterdam flight , but were not seated next to each other . Authorities are still looking into whether the men were traveling together or simply had similar itineraries , the official said . CNN 's Nic Robertson , Jeanne Meserve , Mike Ahlers and Susan Candiotti contributed to this report .
NEW : Men in custody may have been testing security . NEW : The FBI is investigating the incident, but it's unclear if they are looking into whether or not there was a connection between the two incidents. Arrests follow Chicago-to-Amsterdam flight . Dutch investigators keep lid on details .