Security has been tight around the Capitol building
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The Capitol building in Washington - which houses the US Congress - has been re-opened after a security alert.
A suspicious substance discovered in its basement turned out to be an industrial solvent, Capitol police spokeswoman Jessica Gissebel said.
Congress was in holiday recess at the time; an evacuation nonetheless took place.
Samples of the substance have been sent to Johns Hopkins University in Baltimore for further analysis.
The US Congress was a target of anthrax mail attacks
shortly after the 11 September attacks in 2001.