The White House was locked down in an alert on Monday after a man identified as Alexander Sahaghan man threw firecrackers over the outer fence, sparking great concern in the nation's capital, just hours after a shooting spree in Washington D.C. left 13 people dead, AFP reported.

Sahaghan is described as a middle-age white man who had been wearing a blue T-shirt and a pair of shorts, the Secret Service told ABC News. Charges have yet to be filed against him, but is likely to be hit with with "throwing a projectile," ABC News also reported. 

After the firecrackers were hurled by Sahaghan, heavily armed Secret Service teams at the White House scrambled and tackled him outside the gate, news reports said.

The lockdown in the city lasted for almost 30 minutes until the Secret Service deemed that the threat had been cleared. DC had been on edge all day since morning when Aaron Alexis, a US naval reservist, opened fire and went on a massive shooting spree at the Navy Yard, which killed 12 people. Alexis later died in a gun battle with police.

The shooting at the DC Navy Yard marks one of the worst mass shootings in U.S. history.