According to French media, a man was decapitated on a street in the Conflans St Honorine area at about 5pm local time.
The country's anti-terror prosecutor has called the incident a stabbing but the Reuters and AP news agencies reported the victim was decapitated, according to police sources.
A second police source told Reuters that witnesses heard the attacker shout Allahu Akbar, or God is greater.
A terrorism investigation is underway, AP reported.
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