U.S. law enforcement officials say investigators are looking into whether two men arrested in Amsterdam were conducting a dry run for a potential terrorist attack, after they managed to check baggage containing potentially fake explosives onto a United Airlines flight to Chicago. The White House said Tuesday the men were not on any U.S. terror watch list.

One law enforcement official, speaking on condition of anonymity to discuss an ongoing investigation, says the FBI is pursuing leads in Detroit, Birmingham, Ala., and Memphis, Tenn. One of the men, believed to be from the Detroit area, is of Yemeni descent.

Two U.S. officials said investigators are looking into whether this was a dry run for a future terror attack and whether they were testing the aviation security system to see whether strange items and travel patterns would raise suspicion.

The pair was arrested Monday morning at Schiphol Airport in Amsterdam after getting off a United Airlines flight from O'Hare, where their decision to change their flight plans raised flags in the U.S., officials said.

RTL Television News broadcast video footage filmed on a passenger's cell phone of armed law enforcement officers escorting two men off the plane, their hands bound behind their backs. The officers' weapons were holstered and there appeared to be no resistance.

They were being held at the airport for questioning, but neither has been charged with any offense in the Netherlands, said Martijn Boelhouwer, spokesman for the national prosecutor's office. Under Dutch law, the men can be held without charges for up to six days.

"The men are held in custody on suspicion of a conspiracy to a terrorist criminal act," said Dutch public prosecutor Guus Schram. "In a few days, it will be made public if they will be charged."

Sources were telling CBS News shortly after the arrests that at least one of the men, Ahmed Mohammed Nasser al Soofi, may have been testing the U.S. security system.

The two men boarded the Chicago flight last night after taking a plane from Birmingham, Ala., International Airport.

In Birmingham, Al Soofi was singled out for a pat down and was found to have $7,000 in cash, according to federal sources.

Al Soofi's checked baggage set off an alarm as it was being screened. It was searched and found to contain seven cell phones, one of which was taped to a bottle of Pepto-Bismol, as well three cell phones taped together and several watches that were also taped together. These appeared to be "mock explosive devices."

Knives and box cutters were also found.

But Al Soofi and his baggage were cleared to fly on a United flight to O'Hare. He was busted after authorities say he sent his checked baggage to Dulles International Airport outside Washington, D.C., while he himself went on to Amsterdam.

The "mock devices" were cleared as harmless. But aviation attorney and retired Col. John Hoff said they were cause for alarm.

"Anytime anybody has a bunch of cell phones taped to bottles and triggering devices like digital watches, it sounds like something you want to know about," Hoff said.

Hoff added that it seemed fairly clear that the suspects were conducting a dry run for a terrorist attack.

"People are using words like, 'probe,' 'dry run,' 'testing the system,' and apparently, that's what it was," he said.

But some Muslim leaders warned against jumping to conclusions.

"If it's a case of just cell phones and antacid, well, that's kind of really not good enough," said Ahmad Rehab, executive director of the Chicago Office of the Council on American-Islamic Relations.

The bomb-like devices were described as amateurish. Al Soofi was originally ticketed to fly on a United flight from O'Hare to Dulles with connecting flights from there to Yemen, but he changed his itinerary to flights from O'Hare to Amsterdam and then to Yemen.

Two of his four checked bags were put on the flight to Dulles where the suspicious items were found.

"After 9/11, that is rule No 1. that [passengers and bags] go together and not severed that creates opportunities for walk-away terrorism," said DePaul University transportation expert Joe Schwieterman.

Hezem Abdullah Thabi al Murisi was also aboard the flight from O'Hare to Amsterdam and had the same itinerary for flights and had made the same itinerary changes.

The United States notified Dutch authorities, and both men were taken into custody by Netherlands authorities who boarded the plane in Amsterdam.

Federal air marshals were on the flight from Chicago to Amsterdam.

Edmond Messchaert, a spokesman for the National Coordinator for Counterterrorism in the Netherlands, said the organization was aware of the case, but would not comment further.

"We are in the loop. We were informed yesterday that this was going down and we are being kept informed of progress," Messchaert told The Associated Press.

Dutch authorities do not release the names of suspects in criminal investigations and Boelhouwer would not confirm their nationalities. He also declined to say if U.S. authorities had requested their extradition.

Meanwhile, FBI agents on Monday visited the Detroit neighborhood where several addresses were found for variations of al Soofi's name, according to neighbors who declined to give their names to The Associated Press.

Al Soofi's brother, Murad al Soofi, told the Detroit News his brother moved to Michigan from Yemen in 1997. He told the newspaper al Soofi has a wife and five children in Yemen.

Both al Soofi and al Murisi had also previously lived and worked in Dearborn, Mich., and their families were prominent in the Yemeni-American community there, Imad Hamad of the American-Arab Anti-Discrimination Committee told the Detroit News.

Al Soofi moved to Tuscaloosa, Ala., earlier this year, after he lost jobs in Detroit and the suburb of Monroe, his brother told the Detroit News. Murad al Soofi told the newspaper his brother had been flying to Yemen to visit his family, but didn't have an explanation of why he wanted to change flights at O'Hare, the newspaper reported.

CBS 2's Dana Kozlov, Mike Puccinelli and Susan Carlson, and the Sun-Times Media Wire, contributed to this report.