Dutch authorities detained two Yemeni men at Amsterdam's Schiphol airport on suspicion of terrorist conspiracy after a tip-off from the United States.
The pair, en route from Chicago to Yemen, were detained on Monday and a decision on bringing charges is to be made in the next few days, the Dutch prosecution service said.
"The men are being held in custody on suspicion of conspiracy to commit a terrorist criminal act," the prosecution service said in a statement.
The Yemenis arrived in Amsterdam from Chicago O'Hare airport on United flight 908 early on Monday and were detained on the plane after the US Department of Homeland Security alerted Dutch authorities to suspicious items found in their luggage in the United States.
These included mobile phones found taped together, and one phone taped to a plastic bottle. The phones were seized in the United States.
The circumstances of the security alert have prompted some security experts to suggest the men - identified by a US law enforcement official as Ahmed Mohamed Nasser al Soofi and Hezam al Murisi - could have been conducting a test run for a planned terrorist attack.