At least 3,000 Shia-led fighters have arrived near Ramadi in Iraq's western Anbar province, a day after the city's capture by the Islamic State of Iraq and the Levant (ISIL) group.
Iraqi military officials said on Monday the fighters entered Ramadi, the provincial capital, from the south and stationed themselves at a military base there.
"Hashid Shaabi forces reached the Habbaniya base and are now on standby," Sabah Karhout, head of the Anbar provincial council, said.
They were fully equipped and highly capable, according to the provincial council, which comprises tribal leaders. 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.
Meanwhile, US-led fighter jets have stepped up raids against ISIL, conducting 19 air strikes near Ramadi over the past 72 hours at the request of the Iraqi security forces, according to a coalition spokesperson.
At the same time, the US has played down the significance of the fall of Ramadi, however, with John Kerry, the secretary of state, saying that ISIL's offensive would be reversed.
"I am convinced that as the forces are redeployed and as the days flow in the weeks ahead that's going to change, as overall [they] have been driven back... I am absolutely confident in the days ahead that will be reversed," he said during a visit to Seoul, South Korea, on Monday.
The UN said almost 25,000 people have fled Ramadi after ISIL's attack on the city.
Iraq's government had previously asked Shia-led armed groups to prepare to deploy and fight in Anbar after ISIL overran Ramadi, Al Jazeera has learnt.
Al Jazeera's Zeina Khodr, reporting from Baghdad on Monday, said the Shia groups had been asked by the government to lead the counterattack against ISIL in Ramadi.
"They operate under the government-sanctioned Popular Mobilisation Forces and were responsible for pushing ISIL from Diyala and Salahuddin," she said.
Iraqi special forces soldiers reportedly fled Ramadi on Sunday as ISIL fighters succeeded in breaching their last holdout. ISIL had earlier made significant gains in its battle to control Ramadi, besieging the army base and killing 15 soldiers in multiple suicide car-bomb attacks.
Ramadi had been one of just a few towns and cities to remain under government control in mainly Sunni Anbar.
There are concerns, however, that the involvement of Shia fighters in the offensive will alienate some Sunni tribes.
Following the recapture of Tikrit earlier this year, Shia fighters were accused of a range of human-rights abuses.
Tarik al-Abdullah, secretary-general of the Anbar council, told Al Jazeera on Monday that the Shia fighters are "not very welcome".
He said the government should be supplying weapons and training to volunteer fighters in Anbar, instead of using armed groups.
"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.
Against this backdrop of fighting in Ramadi, the International Office for Migration has said that about 8,000 people have been forced to leave the city, while local officials say that 500 people, including civilians, have been killed.
Source: Al Jazeera and agencies