About 1400 people, including tourists and staffs, were evacuated from France's most famous landmark - The Eiffel Tower on Saturday evening, after the local police received a bomb threat from an anonymous caller.
Police said an anonymous call had been received from a phone booth in a Paris suburb warning that explosives had been place around the tower.
The tower was reopened around two-and-a-half hours later after police searches failed to find any suspicious objects.
The anti-terrorism unit is investigating.
French authorities have stepped up counter-terrorism measures in recent weeks amid heightened concern about threats to France over its military campaign against al-Qaeda-linked fighters in Mali which began more than two months ago.
The 1,050ft tall iron lattice tower was built for the 1889 World's Fair, and soon turned into a prestige symbol of modern France.
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