Updated at 9:23 a.m. ET: The U.S. Embassy in Brussels was evacuated for about an hour Wednesday after two vehicles containing gas bottles were spotted nearby, an embassy spokesman said.

The spokesman told NBCNews.com that investigations determined there was nothing “nefarious” about the vehicles and staff were allowed to return.

Earlier, a Belgian Defense Ministry spokesman told Reuters that Belgian bomb disposal experts were investigating the two vehicles.

"As far as I know there are two suspect vehicles, one close to the American embassy and one close to the Belgian Defense Ministry,'' ministry spokesman Didier De Weerdt said before embassy staff were given the all-clear. "Apparently there are gas bottles inside the vehicles.''

Reuters contributed to this report. 

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