A Sudanese-born man was arrested at London's Heathrow Airport early Wednesday on suspicion of possessing ammunition but was later booked on terrorism charges.

The 45-year-old man had just arrived from Washington, D.C., on a Virgin Atlantic flight and was arrested after passing through a security check, according to British officials. He apparently had been en route to the Gulf Arab state of Dubai (search). The U.S. Department of Homeland Security confirmed that the man was born in the Sudan.

Scotland Yard (search) was still questioning the man, who had been in custody about eight hours as of 10 a.m. EST, and would only say that he had been found to be carrying "a quantity of suspected ammunition."

Police officials told Fox News that there were five rounds of suspected ammunition found with the passenger. The man was originally being held under Section 1 of Britain's Firearms Act, which prohibits the possession of firearms or ammunition under certain restrictions, because officials were not yet treating the incident as something terrorist-related.

But London Metropolitan Police later confirmed to Fox News that the Sudanese man was later also booked under Section 41 of the Terrorism Act, which is for "alleged involvement in the commission, preparation, or instigation of an act of terror."

Officials told Fox News that they're trying to determine whether the ammunition was live or something as harmless as a shell casing. They're trying to determine whether the man had the suspected ammunition with him when he boarded the plane at Dulles International Airport in Virginia or whether he got them at Heathrow.

Officials were also looking into an unconfirmed report that the man had overstayed in the United States and was being deported on the Virgin Atlantic flight.

Police sources said the man is not a known terror suspect.

Virgin Atlantic spokeswoman Wendy Buck told Fox News that the aircraft the man flew on never was in danger.

"The safety and welfare of our passengers and crew is Virgin Atlantic's top priority," a statement from the airline read. "The item seized did not pose a threat to our aircraft."

In that statement, Virgin Atlantic noted that it was the responsibility of the U.S. Transportation Security Administration (search) to screen passengers upon boarding in Washington and that it could not comment further on the incident.

London's Metropolitan Police say the man was arrested at 7:40 a.m. British time. He had gotten off Virgin Atlantic's Flight 22, which had arrived at 7:13 a.m. after an overnight flight from Dulles.

Fox News' Catherine Herridge contributed to this report.