The UN Security Council has condemned attacks in Iraq by Islamist militants who have overrun two major cities, Mosul and Tikrit.
The UN also said the humanitarian situation around Mosul, where up to 500,000 people have fled, was "dire and is worsening by the moment".
Iraqi PM Nouri Maliki vowed to fight back against the Islamic State of Iraq and the Levant (ISIS) insurgents.
He also said he would punish troops who fled offering little or no resistance.
The militants are consolidating positions in Tikrit, Saddam Hussein's hometown, which they took on Tuesday, a day after capturing Mosul, Iraq's second city.
ISIS, which is also known as ISIL, is an offshoot of al-Qaeda. It controls a large swathe of territory in eastern Syria and western and central Iraq, in a campaign to set up a Sunni militant enclave straddling the border.
In a statement, the UN Security Council said it "deplored in the strongest terms the recent events in the city of Mosul".
Secretary General Ban Ki-moon called on "the international community to unite in showing solidarity with Iraq as it confronts this serious security challenge".
The Security Council also expressed "grave concern for the hundreds of thousands of individuals who have fled their homes".
"Here’s a forecast: the bad news is just beginning." Dexter Filkins on Extremists' Iraq Rise as America's Legacy: http://t.co/dw7kb02Hts— Philip Gourevitch (@PGourevitch) June 12, 2014
Earlier, Unicef's Iraq representative, Marzio Babille, said the situation in Mosul was "alarming".
"The situation is dire and is worsening by the moment. We have to reach children with safe water, shelter, food, and protection - they cannot wait."
The ISIS fighters swept south from Mosul through Baiji. Baiji hosts the nation's largest oil refinery but that appears to still be in government hands.
The insurgents then moved into Tikrit.