Ramadi battle: Shia militias near IS-held Iraqi city
Shia militias are assembling east of the Iraqi city of Ramadi to prepare for a counter-attack against Islamic State militants who captured it on Sunday.
Iraqi state TV described tanks and other military vehicles entering al-Habbaniyah military camp. IS fighters are reportedly moving towards the base.
The Iraqi government called for help from the Iran-backed militias after the military was routed and fled.
About 500 people died in the city - only 70 miles (110km) west of Baghdad.
Shia forces at Habbaniya, about 20km (12 miles) from Ramadi, were "now on standby," the head of the Anbar provincial council, Sabah Karhout, was quoted by Reuters as saying.
In a statement, the council said about 3,000 Shia fighters had arrived in Anbar to take part in "the liberation of all Ramadi areas in which IS militants took positions".
But IS militants had also advanced from Ramadi to the outskirts of the town of al-Khalidiyah, near the Habbaniyah base, an IS statement and witnesses said.
Analysis: Jim Muir, BBC Beirut
The fall of Ramadi is a disaster for the Iraqi army and government, and especially its Prime Minister, Haider al-Abadi.
After the recapture of another provincial capital, Tikrit, at the end of March, he announced the start of a similar campaign to "liberate" Anbar province (the country's biggest) and flew to Ramadi to kick it off.
Now Ramadi has gone, and along with it the military command centre for the whole province. A few days before the final collapse on Sunday, Mr Abadi said he would not allow it to fall.
Now he and the largely Sunni provincial council have had to do what they didn't want - to call in the Iranian-backed Shia militias who were instrumental on the ground in recapturing Tikrit.
They will play the lead role if Ramadi is to be recaptured. Will the Americans bomb to support them, and help spread Iranian penetration and control in Iraq?
The US admitted on Monday the loss of Ramadi was a setback.
However, the White House vowed US forces would help the Iraqi government take it back.
Pentagon spokesman Col Steven Warren said: "This is a difficult, complex, bloody fight. And there's going to be victories and setbacks. We will retake Ramadi."
The Shia militias, known as the Popular Mobilisation (al-Hashd al-Shaabi), were key to the recapture from IS of another city, Tikrit, north of Baghdad, in April.
But their use has raised concern in the US and elsewhere that it could provoke sectarian tension in Sunni areas such as Ramadi.
The militias pulled out of Tikrit following reports of widespread violence and looting.
In another move, the Iranian Defence Minister, Hossein Dehghan, has arrived in Baghdad on a visit arranged before the latest developments in Ramadi.
The police and military made a chaotic retreat from Ramadi, which has been contested for months, after days of intense fighting.
A statement purportedly from IS said its fighters had "purged the entire city". It said IS had taken the 8th Brigade army base, along with tanks and missile launchers left behind by troops.
An Iraqi army officer told the BBC that most troops had retreated to a military base in the city of Khalidiya, east of Ramadi, despite an order from Prime Minister Abadi for them to stand firm.
The US-led coalition says it has carried out 19 air strikes in Iraq since early on Sunday, including attacks around Ramadi.
However, they appear to have failed to hinder the IS advance there.
Reports said Iraqi forces had fled following a series of suicide car bomb attacks on Sunday.
Four almost simultaneous explosions hit police defending the Malaab district in southern Ramadi. Later, three more suicide bombers drove explosives-laden cars into the gate of the provincial military headquarters, the Anbar Operation Command, officials said.
Anbar province covers a vast stretch of the country west from Baghdad to the Syrian border, and contains key roads that link Iraq to both Syria and Jordan. Ramadi's loss is seen as a severe setback for the government.
IS reportedly controls more than half of Anbar's territory.
Some 8,000 people have been displaced by the latest bout of fighting in Ramadi, according to the International Organisation for Migration.
Troubled history of Anbar province
- Iraq's largest province, which is Sunni-dominated, was occupied by US forces in 2003
- Hostile to the US, fighting quickly broke out between US troops and the region's Sunni insurgents
- The worst battle came in 2004, when thousands died as US troops and coalition forces struggled to take the town of Falluja
- Fighting continued in 2005 and 2006 during which time al-Qaeda in Iraq (AQI) rose to prominence
- The US declared victory in 2007 but AQI remained, resuming attacks in 2011 when US troops withdrew
- Islamic State and other Sunni insurgents currently control much of the province