The UN says nearly 25,000 people have fled from Ramadi since fighters from the Islamic State of Iraq and the Levant (ISIL) captured the Iraqi city from government forces over the past few days.

Residents continue to flee, mainly towards the capital, Baghdad, as thousands of Shia militias were massing around Ramadi to retake the Anbar province's capital city.

ISIL fighters seem defiant as they spread out in anticipation of the fight with Shia militias, who were asked to deploy by the government in the wake of the government forces' defeat.

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Al Jazeera's Zeina Khodr, reporting from Baghdad, said on Tuesday that ISIL fighters in Ramadi were "still very much defiant".

"They tried to advance from their stronghold in Ramadi city, east towards the Habbaniya military base where we understand thousands of Shia militiamen have been gathering to prepare for the counter-offensive," our correspondent said.

"We understand ISIL was not able to reach the base - they did face resistance. But clearly it is a message that this is not going to be an easy fight.

"ISIL is deeply entrenched in Anbar province. It does have support from people in this province and it doesn't just control Ramadi, it controls vast areas of Anbar."

The moves and counter-moves come two days after ISIL overran Ramadi on Sunday, forcing government troops out from one of the few towns and cities that it controlled in the mainly Sunni Anbar province.

At least 3,000 Shia-led fighters arrived near Ramadi in Iraq's western Anbar province on Monday.

The decision to include the Shia militias in the fight to retake the key city has upset many, including tribal elders in Anbar - who believe that the government should be arming volunteer fighters there, not deploying militias.

The White House said on Tuesday that the US led coalition will support the multisectarian ground force in Iraq in its effort to take back the city of Ramadi from ISIL.

White House spokesperson Josh Earnest said it is important for the force to have control and be in command of Iraq.

'Militias not welcome'

Tarik al-Abdullah, secretary-general of the Anbar council, told Al Jazeera on Monday that the Shia fighters are "not very welcome".

"We need the support of the government. We have a big number of volunteers waiting to participate to liberate our province from [ISIL]," Abdullah said.

Meanwhile, the UN said the World Food Programme has distributed thousands of emergency response rations to internally displaced people fleeing Ramadi - enough to last three days.

Other UN agencies, in tandem with international NGOs, are also distributing water and health kits to those displaced by the fighting.

"Within the past month, UN agencies and non-governmental organisations have provided life-assistance to more than 130,000 people who fled Ramadi following ISIL attacks in April," the UN said in a statement.

A senior Iranian official said on Monday that his country was ready to help confront ISIL and that he was certain Ramadi would be "liberated" from their grip.

"If the Iraqi government made an official request to the Iranian government in it's capacity as a friendly and brotherly country to Iraq, which can take on a role to help Iraq to confront these extremist phenomena - then the Islamic Republic will respond to this request," said Ali Akbar Velayati, an adviser to Iran's Supreme Leader Ali Khamenei.