At least seven houses were evacuated after a piece of a rocket-propelled grenade was found in the back yard of a vacant row house.

The Washington Post reports the item was discovered Wednesday afternoon in the Manor Park neighborhood of Washington.

Metropolitan Police Department Chief of Police Cathy L. Lanier says the item was a piece of a shoulder-mounted anti-tank weapon. She says authorities are treating the discovery seriously.

Police did not provide information about how the device was discovered or who found it.

Roads were reopened and residents were allowed to return to their homes around 4:15 p.m. after authorities removed the device for further investigation.