Tens of thousands of people have fled the Iraqi cities of Tikrit and Samarra after they came under attack from Islamist militants, the International Organisation for Migration said Friday, as it warned it is bracing for a drawn-out crisis.
Fighters from the Islamic State of Iraq and the Levant (ISIL) have overrun a succession of major towns and cities over the last week and are closing in on Baghdad.
The IOM, which is based in Geneva, said its sources on the ground estimate 40,000 people have fled militant-held Tikrit and Samarra, which has come under a series of attacks and where militants were gathering Friday for a new attempt to take the city.
The latest figure adds to the half a million people the IOM estimate to have fled Iraq's second city, Mosul, after it was overrun Tuesday.
"Insecurity is spreading across the whole of Iraq and we forsee a protracted humanitarian crisis," IOM emergency coordinator in Baghdad, Mandie Alexander, said in a statement.
Spokeswoman Christiane Berthiaume also stressed the volatility of the situation.
"People are on the move and most of them are fleeing the fighting," she told reporters in Geneva.
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UN human rights chief Navi Pillay expressed alarm Friday at reports the militants were carrying out summary executions and extrajudicial killings, and said hundreds had likely been killed and thousands injured in the violence.
Berthiaume said the situation is desperate for those fleeing insurgent-hit areas, with hospitals in Mosul no longer accessible while drinking water and electricity in many parts of the city are scarce.
"Schools and mosques have been converted into makeshift clinics to tend to the injured and chronically ill," she said.
The UN refugee agency also said Friday that those seeking safety in the Arbil and Dohuk provinces in the north of the country "arrived with little more than the clothes they were wearing."
"Many people have no money, and nowhere to go," spokesman Adrian Edwards told reporters in Geneva.
With some 300,000 people reported to have fled to those two provinces alone, he said that "a shortage of shelter is emerging as a key challenge" in the crisis.
While some people are staying with relatives or at hotels, "many families in Dohuk are also sheltering in schools, mosques, churches and unfinished buildings," he said.
The UN's World Food Programme has launched an emergency operation to bring food aid to some 42,000 of the most vulnerable refugees, which will see nearly 550 metric tonnes of food a month brought into Iraq at a cost of around $1.5 million (1.1 million euros).
The agency is preparing one airlift from Dubai with the rest coming by road from Turkey, spokeswoman Elisabeth Byrs said.