"This is Daesh (an Arabic acronym for the Islamic State group)," Le Pen fired back in a series of tweets picturing grisly IS atrocities.
In one image a bloodied body lay with his decapitated head on his chest, another depicted a man on fire in a cage, while a third showed a victim being driven over by a tank.
Prime Minister Manuel Valls described the photos as "monstrous".
Interior Minister Bernard Cazeneuve alerted the police to look into the tweets "as they do every time these photos are published".
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The photos are "Daesh propaganda and are a disgrace, an abomination and an absolute insult to all victims of ... Daesh," said Cazeneuve.
Le Pen was reacting to comments by BFM journalist Jean-Jacques Bourdin whom she accused of drawing parallels between her National Front (FN) party and Islamic State in an "unacceptable bungle".
Bourdin, during his show known for combative one-on-one interviews, posed a question to Arab world expert Gilles Kepel in which he suggested there were "links" between FN and IS as both sought to push the French to cling to their cultural identity.
In the wake of the November 13 attacks in Paris that left 130 people dead, Le Pen warned that if IS was not conquered "Islamist totalitarianism will take power in our country".