Iraq militias start fightback against IS in Ramadi
About 3,000 militia members in Iraq have begun moving against Islamic State militants after the fall of the city of Ramadi last week, officials say.
The pro-government forces say they have retaken Husayba, east of Ramadi.
Ramadi - the capital of Anbar province - is only 110km (70 miles) west of Baghdad. Its fall was seen as a major embarrassment for the government.
About 500 people died in the city, and more than 40,000 - a third of the population - have fled.
Analysis: John Simpson, BBC World Affairs Editor, Baghdad
It looks very much as though the operation which has begun near Ramadi in Anbar province is being carried out without much involvement by the Iraqi army. Last weekend 200 Islamic State fighters captured Ramadi from 10 times that number of Iraqi army soldiers.
Military observers here maintain that the army simply doesn't have the determination to match the commitment of Islamic State, and that the so-called Popular Mobilisation forces are the only ones with the necessary drive and determination.
There's a problem, though. The majority of the volunteers are Shia Muslims, and there has been anxiety about using them in Anbar province, which is overwhelmingly Sunni. But the groups do contain Sunni fighters as well, and the government maintains they operate under strict control.
The Iranian-backed Shia Popular Mobilisation forces (al-Hashd al-Shaabi) launched their operation out of the Iraqi air base at Habbaniya, about 20 miles (30km) from Ramadi.
A Sunni tribal leader in Anbar, Sheikh Rafia Abdelkarim al-Fahdawi, told AFP news agency that his volunteers had also been deployed - in addition to police, special forces and army troops.
Iraqi police spokesmen told news agencies that IS militants had been driven from Husayba and it was now under the control of pro-government forces.
Ramadi's fall was a massive blow to the Iraqi army, to Prime Minister Haider al-Abadi and to the US, which had encouraged his policy of relying on the official armed forces and police and ruling out a role for the militias, says the BBC's Jim Muir in Beirut.
The Shia militias played a key role in re-capturing another mainly Sunni provincial capital, Tikrit, from IS at the end of March.
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.
IS reportedly controls more than half of Anbar's territory.
The UN says it is trying to reach the civilians displaced from Ramadi.
The largest concentration is at the Bzebiz bridge over the Euphrates, on the road to Baghdad. It was closed by the authorities to prevent those fleeing from entering the Iraqi capital.
There are reports of children dying of dehydration in the heat, UN Deputy Humanitarian Co-ordinator for Iraq Dominik Bartsch told the BBC.
It is unclear why the Bzebiz bridge was closed, though there have been concerns that militants could mingle with the displaced and infiltrate Baghdad.
Very little information is available about those still in Ramadi, Mr Bartsch said.
"We hear stories of reprisals, of shootings, of individual persecution of civilians who have remained in the city."
In addition to Ramadi, this week IS militants have also seized the last Syrian government-controlled border crossing with Syria on Friday and, in Syria itself, the ancient city of Palmyra.
Some observers said IS now controls 50% of Syria's entire territory - as well as a third of Iraq.
On Friday, Iraqi Deputy Prime Minister Saleh al-Mutlaq warned that fighting IS was no longer a "local matter", and called on the international community to act.
An international coalition has been carrying out air strikes against the militants in Iraq and Syria for months.