Police carried out a controlled explosion after being alerted to two unattended vehicles outside the US embassy in Wandsworth.
Officers were called at 4.38pm on Wednesday to Ponton Road in south west London.
A bomb disposal robot was used for the controlled explosion of a red van parked next to the unopened building at 5.37pm.
London Ambulance Service, London Fire Bridage and specialist officers attended.
One of the vehicles belonged to Taus Larsen, 40, who said he was “surprised” when he returned to his Ford van to find that the front passenger side window has been smashed and the back door has been crow-barred.
He said: “In hindsight maybe it wasn’t ideal to have left it here for so long. But there wasn’t any lines.
“I only live around the corner, I Just came back to check up on it. I came here on my bike and thought someone had robbed it.
“I thought the commotions had been because there had been a break-in. It turned out the police had broken in or crow-barred the window, or try to crowbar the back door open.”
Mr Larsen had parked the car on the street on Monday.
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