Harriet McGuire, public affairs officer in the embassy, refused to give details about the threat, which forced the embassy to close its doors Monday. The embassy remained shut Tuesday and it is not clear when it would reopen, she said.
"There was a specific threat. Several things came together," she said in a telephone interview.
A statement released by the embassy on Monday said the closure was ordered to "prevent injuries or loss of life."
The U.S. State Department last month shut down embassies in Gambia, Togo, Liberia, Namibia, Senegal and Madagascar over security concerns. All six embassies have reopened with enhanced security.
The State Department has warned that a group it believes is led by Osama bin Laden - a Saudi exile suspected of masterminding and financing the Aug. 7 bombings of U.S. embassies in Kenya and Tanzania - may be preparing to strike again. The bombings killed 224 people and injured thousands.
The embassy closure comes as the U.S. House of Representatives Tuesday debated a drive to fortify its overseas diplomatic missions with a $2.4 billion foreign affairs funding bill.
In rejecting an anti-abortion amendment introduced by a Republican congressman and voting to fund a United Nations population program, the House eliminated a major obstacle in the bill's passage Tuesday.
In addition to $1.4 billion to protect U.S. embassies around the world from the threat of international terrorism, the bill authorizes $750 million for refugee assistance and additional funds for various other foreign affairs programs.
"Unless we can do something about it, such acts of terrorism are more likely a prelude of things to come," declared Republican Rep. Doug Bereuter of Nebraska.