White House on alert after 'metal object' hurled over fence

Authorities temporarily placed the White House on lockdown Monday after someone threw a metal object over the fence around the presidential mansion, officials said.

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.

"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.