Two men who flew from Chicago to the Netherlands have been held for questioning at Amsterdam’s Schiphol airport after US officials raised suspicions over their luggage, prompting speculation they may have been testing security levels at airports.

Ahmed Mohamed Nasser al Soofi and Hezam al Murisi were found with a mobile phone taped to a medicine bottle, a knife and a box cutter hidden in their luggage.

Air marshals were placed on the United Airlines flight after U.S. authorities noticed the “suspicious items” in their luggage.

U.S. officials asked Dutch police to detain the men after they arrived at Schiphol airport with the “mock bombs”.

Security officials questioned Al Soofi as he went through security in Alabama on his way to Chicago but the men have not been charged with anything in the U.S.

He told the Transportation Security Administration authorities he was carrying a lot of cash.

Security officials found US$7,000 on him, but he was not breaking any law by carrying that much money.

Officials also found several mobile phones and watches taped together in his checked baggage.

Al Soofi is believed to be originally from Yemen. He was supposed to fly from Chicago to Washington Dulles International Airport in Virginia, and then on to Amsterdam. But when he got to Chicago, he changed his travel plans to take a direct flight from Chicago to Amsterdam.

Al Murisi also changed his travel plans in Chicago to take a direct flight to Amsterdam, raising suspicion among U.S. officials.

The men are likely to appear in court later before a judge, who will decide whether they should be released or remanded into custody pending possible charges of preparing a terrorist attack.

The trigger for the detention request appears to have been their flight a Delta Airlines flight bound for Amsterdam when their luggage was discovered to be checked into a separate flight to Dubai. However, no explosives were found in the luggage, prompting the speculation that the men may have been conducting a test of airport security.

Security at Schiphol airport has been raised since Umar Farouk Abdulmutallab, a Nigerian student, boarded a Northwest Airlines flight to Detroit at Schiphol with 80 grams of explosive in his underwear on Christmas Day 2009. He is on trial for attempting to blow up the plane.