This is not the first time White House security has been tested. In this IBTimes UK video a US Secret Service Director faces criticism over security breaches.IBTimes UK

The White House has returned to "normal operations" after a lockdown was triggered when a metal object was thrown over an outer fence of the premises, say officials. The partial lockdown of the President's official residence was activated at around 12.15pm on Monday (30 May).

A spokesman for White House security said that a woman had been arrested immediately "without incident" and that hazardous material checks had been made with "negative results". The lockdown took place during the nation's Memorial Day holiday, while President Barack Obama was reportedly inside the building.

Earlier Obama had visited the Arlington Cemetery as part of the annual commemoration for armed services members. Spokesman Shawn Holtzclaw said in a statement: "An individual threw a metal object over the north fence line at the White House.

"Secret Service Uniformed Division officers immediately apprehended the individual without incident. All protective sweeps of the metal object were met with negative results, the statement added.

Emergency services, including police, fire trucks and the hazardous materials response unit rushed to the scene. The area inside the fence was swept afterwards whilst reporters inside the White House were forbidden to leave.

Last month, the White House was put into lockdown twice in 24 hours after someone threw a package containing a mobile phone and paper over the fence. The day before someone had attempted to leap over the fence after fleeing a crime scene, causing a security lockdown.

In 2015, the White House was placed under high security alert on Thanksgiving Day after a man draped in a US flag jumped over the fence while Obama and his family were in residence. Joseph Caputo climbed over the fence on the north side of the complex and stood on the North Lawn before he was arrested.

And, in February 2015, the White House went into lockdown after secret service agents found a suspicious package in a nearby park, triggering a bomb alert.

The White House
A member of the U.S. Secret Service Uniform Division guards an entrance of Lafayette Square in front of the White HouseAFP/Getty