The churches are the only Christian houses of worship that serve the city’s Christian population, Alsumaria news network reported.
The fighters invaded the churches, destroyed all crosses, burned the altars, and caused severe damage to the properties.
The fighters raised the flag of ISIL (a variation of Al-Qaeda’s flag) atop the churches and then proceeded to torch them.
The European Union Special Representatives have also reported that ISIL blockaded the streets and raped at least five women.
Local residents have left their houses on fear of more rids by the ISIL terrorists, the EU watchdog added.
U.N. human rights spokesman Rupert Colville also on Friday highlighted disturbing reports including the suicide of four women after being raped by ISLI militants.
He said his office had reports the killings included the execution of dozens of civilians working for the police and a court employee in central Mosul by ISIL militants.
Four women had killed themselves after being raped or forced to marry ISIL militants, 16 Georgians had been kidnapped, and prisoners released by the militants had been looking to exact revenge on those responsible for their incarceration, he added.
The UN's human rights chief also expressed alarm on Friday at reports of extrajudicial killings and summary executions in Iraq as militants advance across the north, warning that civilians were particularly at risk.