Twitter Police have launched a probe after a man with a knife burst into the Eiffel Tower

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French prosecutors have opened a counter-terrorism investigation after the incident late on Saturday at around 2130 GMT. The young French man, who is the main suspect in the case, was recently discharged from a psychiatric hospital and is under investigation for "glorifying terrorism" after he brandished a knife, a judicial source said. The security breach was initially treated as a criminal matter, but was later designated a counter-terrorism case because of the suspect's statements to police and his apparent radicalisation, the source said.

No one was hurt, although the tower was briefly evacuated. Twitter users took pictures of worried tourists fleeing for their lives after the incident. And, a judicial official said that when the man tried to force his way into the secure zone, he held out a knife and said “Allahu akbar,” the Arabic phrase for “God is great”. But he was quickly surrounded by security forces and surrendered, the official said.

Eiffel Tower evacuated: Pictures from the scene Sun, August 6, 2017 Play slideshow EPA 1 of 5 The Eiffel Tower in Paris

Twitter Tourists flee from the scene of the Eiffel Tower after it was closed off last night

A Paris police official said no shots were fired. The judicial official added that the incident was initially being investigated as a common crime and not by anti-terrorism investigators. This was because of the suspect's history of psychiatric problems and because authorities had no reason to believe he was part of a network or planning an attack. However, this changed on Sunday.

Twitter French prosecutors have opened a counter-terrorism investigation after the incident