Reporters working at the White House said a woman had been arrested.
"An individual threw a metal object over the north fence line at the White House," the Secret Service said in a statement after the approximately three-hour lockdown ended.
Armed man shot outside White House
"Secret Service uniformed division officers immediately apprehended the individual without incident."
Officials said they conducted "protective sweeps" of the object but determined it was not a threat.
"The White House has returned to normal operations," the Secret Service said.
President Barack Obama had been attending a Memorial Day service at Arlington National Cemetery when the incident occurred.
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