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WASHINGTON (Reuters) - A security lockdown at the White House triggered by a loud bang just as President Barack Obama was due to leave was caused by a souvenir truck catching fire in a nearby street, the Secret Service said on Saturday.

The security alert happened just moments before Obama and his family had been due to board a helicopter from the presidential mansion’s South Lawn for Andrews Air Force Base.

Secret Service spokesman Brian Leary said the fire had been contained and a vehicle near the White House was investigated and cleared after a bomb-sniffing dog detected something on it.

Obama and his family left the White House by motorcade instead of helicopter an hour later and boarded Air Force One at Andrews Air Force Base.

The Obamas are traveling to Selma, Alabama, to commemorate the 50th anniversary of a civil rights march.

Several streets around the White House were closed for a few hours but reopened soon after noon. White House tours were also interrupted but resumed in late morning after the vehicle identified by the dog team was cleared, the Secret Service said.

The souvenir truck, which belonged to a Korean family from Virginia who do not speak English, was completely destroyed by the fire, according to a Reuters reporter at the scene.

Over the past few months, the White House has come under several lockdowns, mostly caused by intruders jumping the fence.