Amsterdam, Netherlands (CNN) -- Two men arrested at Schiphol International Airport in the Netherlands are being held on suspicion of plotting a terrorist act, Dutch authorities said Tuesday.
They are Yemeni citizens who were en route to the Yemeni capital, Sanaa, from Chicago, Illinois, officials said.
They were arrested Monday morning and authorities continued to question them Tuesday, Dutch prosecutors said.
A U.S. law enforcement source said Monday the men may have been trying to test U.S. airport security by putting bottles attached to electronic devices in their checked baggage.
But two U.S. government officials said Tuesday an initial U.S. investigation into the men shows no evidence of terrorism and no indication the men even knew each other.
"This looks like nothing," said one of the officials, saying both men missed flights in Chicago because of a gate change and their airline rebooked them onto the same plane.
"We see no evidence of a dry run or a connection to terrorism," said the source, who is not authorized to discuss the case with the media and asked not to be named.
The Department of Homeland Security noted that the two men "have not been charged with any crime in the United States" and cautioned "against jumping to any conclusions." Appropriate airport security protocols were followed, the department said.
"In this instance, sound judgment led to suspicious items being identified, which triggered automatic security responses by U.S. security personnel," the department said. " ... When the investigation tells us more, we will let you know, but we don't have anything else at this time."
An announcement about whether the men will be charged will be made "in a few days," Dutch authorities said in a statement.
The men were still being held at Schiphol Airport on Tuesday, said Martijn Boelhouwer, a spokesman for Dutch prosecutors.
Another U.S. official said the Dutch are being cautious and checking everything.
That official, who also asked not to be named, said the United States is doing the same and is continuing to investigate.
The U.S. Department of Homeland Security said Monday the two 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.
Dutch authorities confirmed that one phone was found taped to a bottle and seized in the United States. Nothing else suspicious was found in the men's luggage, the Dutch said.
The items have 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, but they are allowed in checked bags.
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.
A co-worker of al-Soofi said he was not known to express anti-American opinions and was "not a very good Muslim" because he drinks beer.
Al-Soofi had been back to Yemen at least twice before to deliver money and gifts, and bought watches and cell phones as gifts for family members on this trip, said co-worker Ali Moqbel in Tuscaloosa, Alabama.
Al-Murisi was scheduled to fly from Chicago to Yemen, with connections in Washington and Dubai, a U.S. government official said, but his flight was changed to go from Chicago to Amsterdam.
Another U.S. law enforcement official said both men were in the United States legally.
That official said neither of the passengers was carrying items that are barred from aircraft, and federal air marshals 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 Washington Dulles International Airport 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.
CNN's Atika Shubert, Nic Robertson, Carol Cratty, Jeanne Meserve, Mike Ahlers, Dave Mattingly and Susan Candiotti contributed to this report.