The attack came amid Quebec's heated debate over the government's controversial proposal to prevent public employees in the workplace from wearing religious symbols like the Muslim hijab.
Marois told reporters in Montreal on Tuesday that the attack on the mosque in the Saguenay region was ''unacceptable.''
She said Quebec is a place where people are capable of respecting diversity.
A letter filled with anti-Islamic rhetoric was also sent to the mosque and to a local, French-language CBC station in the city nearly 500 kilometres northeast of Montreal.
The letter also stated the red liquid splattered outside the building was pig's blood.
Members of the small Muslim community say they believe it was an isolated incident.
The co-founder of the mosque says he believes the actions are the work of "fanatics" and "unbalanced people" who are not representative of the citizens of Saguenay.
Local police say they are investigating the incident.
A leaked copy of the PQ's plan for its Charter of Quebec Values suggests it wants to prohibit public employees from wearing religious symbols like turbans, kippas, hijabs and visible crosses.
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