Dutch prosecutors say two Yemeni citizens who arrived in Amsterdam on a flight from the United States are suspects in a conspiracy to commit a terrorist act.

Prosecutors said the two men flew in from Chicago on Monday and were bound for Sana'a, the Yemeni capital. They were detained due to information provided by U.S. authorities.

Their luggage was sent on an internal flight to Washington, where U.S. authorities found suspicious items. But Dutch authorities said nothing suspicious was in the luggage that arrived in Amsterdam.

Prosecutors said Tuesday the men were being held "on suspicion of a conspiracy to a terrorist criminal act." It will be announced in a few days if they will be charged.

Investigators said the men, who live in the Detroit area, had a cell phone taped to a Pepto-Bismol bottle and a knife and box cutter in their checked luggage.

A U.S. government official, however, said the FBI's investigation of the two detained men is finding that it's unlikely they were on a test run for a future terror attack, even as Dutch authorities continued to hold the pair.

The U.S. official said the two men arrested in Amsterdam did not know each other and were not traveling together.The U.S. does not expect to charge the men, a law enforcement official said. The two men arrested in Amsterdam -- both traveling to Yemen -- did not know each other and were not traveling together, the official said.

The official, speaking on condition of anonymity to discuss the ongoing investigation, says both men missed flights to Dulles International Airport from Chicago, and United Airlines then booked them on the same flight to Amsterdam. The men were sitting near each other on the flight.

Another U.S. official, who also spoke on condition of anonymity, says that when Customs officials discovered one passenger was not on the flight from Dulles to Dubai, they called the plane back to the gate and removed his luggage. It was then they discovered suspicious items in his bag.

Earlier, U.S. officials said they were investigating whether the two men had been conducting a dry run for a potential terrorist attack. But as the probe evolved, officials said that appeared unlikely.

The pair were arrested Monday morning at Schiphol Airport after getting off a United Airlines flight from Chicago, where their decision to change their flight plans raised flags in the U.S. that they were potentially assessing the aviation system for a potential future terror attack

Kip Hawley, the former Transportation Security administrator, said it is not unusual to find items like watches and cell phones bound together on flights to countries like Yemen. He said this would always catch the screener's eye. In 2007, TSA alerted screeners that suspicious items found at U.S. airports may indicate that terrorists were conducting dry runs. Screeners are deliberately on the lookout for such items.

None of the items found on the men or in their luggage violated U.S. security rules. But the items and the men's changing travel itinerary raised concern that it may have been a deliberate test of the U.S. aviation security system to determine what would raise red flags.

A U.S. official identified the men as Ahmed Mohamed Nasser al Soofi and Hezam al Murisi. Al Soofi had a Detroit address. Alabama's director of homeland security, Jim Walker, said he had been living in Tuscaloosa, Ala., and working at a convenience store for about the last three months. He said there was nothing that al Soofi had done in Alabama that brought him to the attention of Alabama officials. 

Al Soofi was questioned as he went through security in Birmingham, Alabama, on his way to Chicago, one of the officials said. He told the Transportation Security Administration authorities he was carrying a lot of cash. Screeners found $7,000 on him, but he was not breaking any law by carrying that much money.

Officials also found multiple cell phones taped together and multiple watches taped together in his checked baggage. It is not illegal, however, to carry knives or taped cell phones and watches in checked baggage.

Al Soofi was supposed to fly from Chicago to Washington Dulles International Airport in Virginia and then on to Amsterdam, the official said. But when he got to Chicago, he changed his travel plans to take a direct flight to Amsterdam.

Al Murisi also changed his travel plans in Chicago to take a direct flight to Amsterdam, raising suspicion among U.S. officials. Federal Air marshals were on the flight from Chicago to Amsterdam, a law enforcement official said.

Homeland Security spokeswoman Amy Kudwa said once officials found suspicious items in luggage associated with two passengers on Sunday night's flight, they notified the Dutch authorities.

"The items were not deemed to be dangerous in and of themselves," Kudwa said. She would not identify the passengers.

Security at Amsterdam's main airport has been boosted this year, after Umar Farouk Abdulmutallab, a Nigerian student, flew from Schiphol airport to Detroit on Christmas Day with explosives in his underwear. Abdulmutallab allegedly tried to detonate the explosives over the United States before being grabbed by passengers and crew.

After the Abdulmutallab security lapse, Schiphol ordered 60 new full body scanners to screen passengers flying to the United States. Those who do not pass through the scanners are patted down.

American passengers arriving from the United States on Tuesday appeared to take the news of the arrests in stride.

"There is always going to be problems but I think that the system in terms of security works pretty well. I am traveling all the time and I feel pretty safe," Steve Harriot of Chicago told AP Television News.

"I think we have to be vigilant, all of us. It is not going to change my travel," Francois Binette of San Francisco said.

The Associated Press and Fox News' Catherine Herridge and Marla Cichowski contributed to this report.