The Eiffel Tower, France's top tourist draw, was evacuated on Sunday and the area ringed by security forces.
A police source said the action followed a threat delivered over the telephone but did not give any details.
Evacuations have been staged regularly at the Paris landmark, usually after bomb threats. There have been two such incidents this year on March 30 and August 9.
On June 18 the monument was closed for two hours after a man threatened to commit suicide.
The Eiffel Tower is the world's most visited monument attracting up to 32,000 tourists daily.
[Image via AFP]