It said the humanitarian situation around Mosul, where up to 500,000 people have fled, was "dire and is worsening by the moment".
Government forces have stalled the terrorists' advance near Samarra, a city just 110km (68 miles) north of Baghdad.
The extremist insurgents, led by an al-Qaeda offshoot called the Islamic State of Iraq and the Levant (ISIL), have been consolidating positions in Tikrit, Saddam Hussein's hometown, which they took on Wednesday, after capturing Mosul, Iraq's second city.
Forces led by ISIL also control a large swathe of territory in eastern Syria and western and central Iraq, in a campaign to set up a militant enclave straddling the border.
UN Secretary General Ban Ki-moon has condemned the acts carried out by the militants, calling on the international community to support the Iraqi government’s fight against Takfiris.
According to reports, Takfiri groups are reportedly entering Iraq from neighboring Syria and Saudi Arabia to undermine security in the country.
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