File Photo: The U.S. flag is unfurled at sunrise as part of the 17th annual September 11 observance ceremony at the Pentagon in Washington, U.S., Sept. 11, 2018. (Xinhua/REUTERS)

WASHINGTON, Oct. 2 (Xinhua) -- Pentagon on Tuesday confirmed that "a suspicious substance" contained in mail to its facility has been detected.

At least two envelopes sent to the Pentagon mail facility have initially tested positive for ricin, local media quoted Pentagon officials as saying.

"On Monday, the Pentagon Force Protection Agency detected a suspicious substance during mail screening at the Pentagon's remote screening facility," Pentagon spokesman Col. Robert Manning said in a statement Tuesday afternoon.

The envelopes were addressed to an individual at the Pentagon, Pentagon spokesman Christopher Sherwood said.

The FBI is expected to conduct a second test to confirm the initial finding, said local media reports.

Pentagon's mail facility is located in a separate building on the grounds of the Pentagon, instead of within the Pentagon building itself.

Ricin, a poison found in castor beans, can be used in powder, pellet, mist or acid form. If ingested, it causes nausea, vomiting, internal bleeding of the stomach and intestines and can be deadly.