Neither of the two men, reportedly US residents, was on any watch lists.
Two Yemenis who arrived in Amsterdam on a flight from the US are being held on suspicion of conspiracy to commit a terrorist act, Dutch prosecutors say.
The men were detained on arrival at Schiphol airport on Monday after police were notified by the US authorities of "suspicious" items in their luggage.
One checked-in bag reportedly contained a mobile phone strapped to a medicine bottle, as well as knives and watches.
But US officials warned against "jumping to any conclusions".
There had been speculation that the two men might have been conducting a dry-run for a potential attack.
But the officials said the incident could have been a case of misunderstanding.
"This matter is under investigation but as of right now, these two passengers have not been charged with any crime in the United States and we caution you against jumping to any conclusions," the US Department of Homeland Security said in a statement.
Under Dutch law, the men can be held without charge for up to six days.
'Vigorous investigation'At a news conference in Amsterdam, Dutch Public Prosecutor Theo D'Anjou said the two men had been arrested by border police shortly after their United Airlines flight 908 from Chicago O'Hare landed at Schiphol on Monday.
Dutch Public Prosecution spokesman Theo D'Anjou: "One phone was found taped to a bottle"
"The arrest took place based on information provided by US authorities. The two men had Yemeni nationality; they were supposed to be travelling to Sanaa. The luggage of the men ended up on an internal flight to Washington," he said.
"In this luggage, mobile phones were found and one phone was taped to a plastic bottle. These phones were seized in the US and have stayed there."
Mr D'Anjou said the luggage with which the men flew to Amsterdam was searched and nothing suspicious was found.
"The men are being held in custody on suspicion of conspiracy of a terrorist criminal act. In the next few days we will make public whether they will be charged," he said.
The US would be kept informed about the progress of the investigation, but no further details could be made public, he added.
"We're going to do a vigorous investigation to see if we can match up any of the circumstances that were involved with any intelligence that we might have," White House spokesman Robert Gibbs told CNN.
"The intelligence community and law enforcement are busy looking through all of these events as we speak," he added.
Air marshalsNeither of the two men, reportedly US residents, was on any watch lists.
One of them was questioned on Sunday as he went through security in Birmingham, Alabama, on his way to Chicago O'Hare. He was reportedly stopped because of his "bulky clothing".
“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”- US Department of Homeland Security
He later told officials from the US Transportation Security Administration that he was carrying a lot of cash, according to AP. Screeners found $7,000 on him, but he was not breaking any law by carrying that much.
When his luggage was searched, security staff found one mobile phone taped to a bottle of Pepto-Bismol, three other mobile phones taped together and several watches, also taped together. A box-cutter and three large knives were also found, according to ABC News.
Officials said there was no indication of explosives, so he and his luggage were cleared for the flight to O'Hare.
At O'Hare, both he and the second man reportedly checked their luggage onto a flight bound for Sanaa, which was scheduled to stop at both Washington Dulles International Airport and Dubai.
But they then decided to take a direct flight to Amsterdam instead. After security staff realised that they had not boarded the flight to Dulles, they ordered the plane back to the gate and retrieved their luggage.
"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," said Amy Kudwa, a spokeswoman for the Department of Homeland Security.
Dutch and US authorities have been on alert since a Nigerian man was detained in the US on Christmas Day 2009 after flying from Amsterdam to Detroit and charged with trying to detonate a bomb.
NBC News reported that US concern about the latest incident was "low", but the authorities wanted to make sure this was not an attempt to test airline security prior to a future attack.
The New York Times quoted a man who said he was one of the passenger's cousins and that there was an innocent explanation.
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