The number of Iraqis fleeing fighting in western province of Anbar has risen to 140,000, the UN refugee agency UNHCR says, citing Iraqi government figures.
In the past week alone, some 65,000 had fled, a UNHCR spokesman said - the largest displacement since the peak of sectarian violence in 2006-2008.
Sunni militants linked to al-Qaeda have seized control of Falluja and parts of Ramadi, the two main cities in Anbar.
This came after security forces cleared Sunni protest camps on 30 December.
Sunni militants allied to the Islamic State in Iraq and the Levant (Isis), as well as armed tribesmen angry with the government, overran Falluja in early January after clashes triggered by a raid on protest camps there and in Ramadi, the provincial capital.
Iraq's minority Sunni Arab community has long complained that it is being marginalised by Prime Minister Nouri Maliki's Shia-led government and unfairly targeted by the security forces.
Most of those displaced by the violence in Anbar have fled to Baghdad and other nearby provinces, but some have travelled as far as the northern Kurdish region, the AFP news agency quoted a UNHCR spokesman as saying.
Correspondents say a government drive to restore control of the two predominantly Sunni cities of Falluja and Ramadi is being seen by many Sunnis as an attempt at domination and oppression.