A petrol bomb has been thrown at the building housing French far-right presidential candidate Marine Le Pen’s campaign headquarters, Paris police said.
A small fire broke out after the device hit an insurance office on the ground floor, where Ms Le Pen’s campaign is based, overnight on Wednesday.
But the Paris fire department said no-one was injured in the incident overnight and the blaze was quickly extinguished. An investigation is under way.
Police said vandals also scrawled graffiti targeting Ms Le Pen’s anti-immigration National Front party.
Ms Le Pen said on France-2 television on Thursday that she suspects extreme-left activists were behind the incident, but added that her campaign has not been contacted by investigators.
Ms Le Pen is a leading contender for France’s presidential election, held in two rounds on April 23 and May 7.