U.S. authorities say a man, detained near the Defense Department headquarters with a backpack of suspicious items, is a member of the Marine Corps Reserve.

The man has been identified as Lance Corporal Yonathan Melaku, a 22-year-old U.S. citizen originally from Ethiopia.

A U.S. Park Police spokesman told reporters Friday that Mr. Melaku was discovered overnight inside Arlington National Cemetery, not far from the Pentagon just outside Washington, D.C.

News reports quote unnamed officials as saying he had an unknown quantity of what may have been ammonium nitrate, which can be used in explosives. But a Federal Bureau of Investigation counterterrorism agent said the man was carrying a backpack containing suspicious items, including a non-explosive, unknown material that she said would require further investigation.

ABC News reported the backpack also contained written material mentioning al-Qaida and the Taliban.

Officials said a search of the man's nearby vehicle did not turn up anything suspicious and no charges have been filed against him.

The park police spokesman said the man was initially “not very cooperative” in answering questions about his activities. He reportedly ran from police before being detained.

Officials closed major roads around the Pentagon during the investigation.