WASHINGTON- A piece of mail delivered to the Pentagon mail facility has initially tested positive for ricin, according to two US defense officials.

The mail facility is in a separate building on the grounds of the Pentagon and the piece of mail which tested positive never entered the Pentagon building.

The FBI and the Pentagon Force Protection agency are responding and further testing is expected to be done by the FBI, the officials said.

Ricin is a highly toxic compound that is extracted from castor beans and has been used in in terror plots.

This story is breaking and will be updated.

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