The Senate's most senior member on Thursday defended Sen. Mark Dayton's (search)  decision to close his Washington office over concerns about a terrorist attack.

"Senator Dayton took this precautionary step based on his conscience and his responsibility to his staff," said Sen. Robert Byrd (search), an eight-term Democratic senator from West Virginia. "I commend him."

Byrd, 86, said in a statement that law enforcement and intelligence experts have warned senators about increased threats to the Capitol in recent weeks.

"They have urged senators to be prepared to have their staffs work from alternate locations," Byrd said. "Senators ought not take these warnings lightly. And those senators who put in place prudent security measures should not be mocked."

Law enforcement officials have said this week that the threats did not specify the Capitol.

Dayton, D-Minn., has been criticized for his decision to close his office while Congress is out of session through Election Day (search). Republicans, in particular, say the move sends the wrong message that Americans can be cowed by terrorist threats.

Dayton has said a recent top-secret intelligence report made him fear for the safety of his staff, and that it would be unfair to jeopardize their safety while he wasn't in the Capitol to share the risk.