Two men removed from a Chicago-to-Amsterdam United Airlines flight in the Netherlands have been charged by Dutch police with "preparation of a terrorist attack," ABC News reports.

The U.S. network quotes U.S. law enforcement officials as saying the two appeared to be travelling with what were termed "mock bombs" in their luggage. "This was almost certainly a dry run, a test," said one senior official.

A spokesman for the Dutch public prosecutor, Ernst Koelman, confirmed the two men were arrested Monday and said "the investigation is ongoing." He said the arrests were made "at the request of American authorities."

The two were allowed to board the flight at Chicago's O'Hare airport Sunday night despite security concerns surrounding one of them, a U.S. official said.

The men were identified as Ahmed Mohamed Nasser al Soofi and Hezem al Murisi. The official said al Soofi had a Michigan address, but no further details about the men were provided.

Al Soofi was supposed to fly from Chicago to Washington and then on to Amsterdam, but changed his plans in Chicago to take a direct flight to Amsterdam, the official said. Al Murisi also changed his travel plans in Chicago to take the same direct flight, raising suspicion among U.S. officials.

The official said a cellphone taped to a Pepto Bismol bottle and a knife and boxcutter were found in luggage alleged to belong to al Soofi, prompting them to alert Dutch authorities.

Homeland Security spokeswoman Amy Kudwa said none of the items found were considered dangerous "in and of themselves."

With files from The Associated Press