Iraqi security forces backed by local tribesmen have been fighting Sunni militants linked to al-Qaeda for control of two cities in the west of the country, Ramadi and Fallujah.
Iraqi security forces backed by local tribesmen have been fighting Sunni militants linked to al-Qaeda for control of two cities, Ramadi and Fallujah, in the large western province of Anbar. Here is a guide to what's happening.
It is the latest development stemming from the year-long Sunni-led protest movement against the government of Shia Prime Minister Nouri Maliki.
What's going on?
Why has fighting broken out?
In short, the government lost control of the strategic cities of Ramadi and Fallujah, to the west of Baghdad.
Tensions were raised on 28 December, when security forces arrested the prominent Sunni Arab MP Ahmed al-Alwani in Ramadi, triggering a gunfight that left six people dead.
In Fallujah, Sunni militants from an al-Qaeda-affiliated group, Islamic State in Iraq and the Levant (ISIS), joined forces with armed men from leading anti-government Sunni tribes and took over.
Two days later, the prime minister ordered troops to dismantle a long-standing Sunni anti-government protest camp in Ramadi, claiming it had "turned into a headquarters for the leadership of al-Qaeda". There was a violent response from Sunni militants. Some 40 MPs, most of them Sunni, offered their resignations in protest at the raid and called for the withdrawal of the army from urban areas, along with Mr Alwani's release.
In nearby Ramadi anti-government Sunni tribes also took charge after the army withdrew amid rising anti-government sentiment. Some militants, possibly linked to ISIS, have been trying to assert their control in a few parts of Ramadi, but are being challenged by the tribes.
On 31 December, Mr Maliki agreed to withdraw the army so that the police could resume control of security. But as soon as soldiers left their posts, militants appeared on the streets of Ramadi, Fallujah and Tarmiya, storming police stations, freeing prisoners and seizing weapons. The prime minister reversed his decision the next day However, they have been unable to regain full control of Ramadi and Fallujah.
Members of Iraq's Sunni Arab minority community have been protesting for more than a year about what they perceive as discrimination by the Shia-led government and unfair targeting by the security forces. Many have also been complaining about the government's inability to provide basic services like electricity and sewerage, largely due to corruption.
But there's always violence, so why is this so important?
Large-scale demonstrations began across Anbar province in December 2012 after security forces raided the home and offices of one of the country's highest-ranking Sunni politicians, then Finance Minister Rafi al-Issawi, and arrested 150 people. Although Mr Issawi was not himself detained, the move came a year after the Sunni Vice-President, Tariq al-Hashemi, was forced to flee the country after a similar raid that followed the withdrawal of US troops. He was subsequently sentenced to death in absentia after being convicted of terrorism charges he denied.
Anbar is Iraq's biggest province, has a Sunni Arab majority and borders Syria, Jordan and Saudi Arabia.
Following four months of demonstrations, gun battles erupted in several predominantly Sunni cities after security forces dismantled a Sunni protest camp in the northern town of Hawija, triggering clashes with gunmen that left more than 40 people dead.
It is the first time insurgents have controlled territory in Anbar province since 2004, when they were driven out by US-backed Iraqi troops.
Extremist Sunni militants aligned to al-Qaeda-affiliated Islamic State in Iraq and the Levant (Isis) subsequently stepped up attacks across the country, targeting security forces personnel, government officials and Shia civilians in hundreds of car bombings and suicide attacks. Meanwhile, Shia militant groups began deadly reprisals on Sunni clerics, civilians and pro-government militiamen. At least 8,868 people, including 7,818 civilians, were killed in attacks in 2013, according to the UN.
The takeover is a serious threat to the authority of Prime Minister Nouri Maliki and a major setback to efforts to quell sectarian violence in Iraq, which has seen an upsurge since US troops completed their withdrawal two years ago.
In an effort to stem the sectarian violence, the security forces have launched campaigns targeting al-Qaeda and its allies. But the crackdown, which took place mostly in Sunni areas and saw the arrest and alleged torture of hundreds of Sunni men, has further enraged Sunnis.
Sunni Arabs, a minority in Iraq but who held power under Saddam Hussein, have long complained of discrimination by Mr Maliki's Shia-led government and of being targeted by the security forces.
How strong is al-Qaeda in Anbar?
Ramadi and Fallujah have about one million people between them and the loss of these two key cities would embolden militants and disgruntled Sunni communities and threaten the unity of Iraq.
Sunnis, particularly those in Anbar province, played a key role in helping the US military turn the tide against al-Qaeda in Iraq in 2007. Alienated by its extremist ideology and harsh methods, Sunni tribesmen formed Sahwa, or Awakening Councils, with US backing and drove al-Qaeda-linked fighters out of their towns and villages north and west of Baghdad.
Anbar was at the heart of the insurgency which followed the US-invasion of Iraq in 2003 and resistance there has never been extinguished.
However, the Iraqi government stopped supporting the Sahwa after the US withdrawal and al-Qaeda slowly regained the ground it had lost. The conflict in neighbouring Syria, where jihadist rebel groups have become increasingly prominent, has been exploited by al-Qaeda. Isis has been able to build some support and attract fresh recruits in Sunni areas of Iraq, as well as establish strongholds across the border in northern and eastern Syria, out of the reach of Iraqi security forces.
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It has also increased its presence in Anbar, setting up training camps, bases and weapons caches. Before the recent fighting, there had been signs of growing public support. One video from November showed a small crowd in Ramadi cheering as Isis members took part in a parade. However, once the militants attempted to seize control of the city, the government was able to quickly strike a deal with tribes to oust them.
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What triggered the unrest?
The immediate catalyst was the break-up by troops of a year-old Sunni protest camp in Ramadi at the end of December 2013. Mr Maliki said the camp had "turned into the headquarters for the leadership of al-Qaeda".
There was a violent response from Sunni militants, and to defuse the situation Mr Maliki agreed to withdraw the army from urban areas.
However, as soon as soldiers left their posts, militants appeared on the streets of Ramadi, Fallujah and Tarmiya, storming police stations, freeing prisoners and seizing weapons.
Mr Maliki reversed his decision the next day but troops were unable to regain full control of Ramadi, while government officials acknowledged that Fallujah was outside state control.
How did militants manage to take over in Fallujah?
Anbar province borders Syria, and in recent months fighters from the branch of ISIS in Syria have crossed into Iraq and helped fuel the insurgency there, according to the Iraqi government.
Al-Qaeda in Iraq, the forerunner of ISIS, was almost stamped out after its defeat in 2004, but it established itself in Syria after the conflict broke out there and is now the strongest jihadist rebel group there.
ISIS has been able to establish strongholds across the porous border in northern and eastern Syria, out of the reach of Iraqi security forces.
Anti-government Sunni tribes in Fallujah sided with ISIS, facilitating their takeover, viewing the militants as fellow Sunnis who support them in their struggle against the Shia-led government. However in Ramadi there is a semi-consensus among Sunni tribes to stand up to ISIS who they regard as terrorists who tarnish the image of the Sunni heartland.
Will the government be able to regain control?
Will the government be able to regain control?
There is no doubt that al-Qaeda is a massive threat to security in Iraq. Foreign Minister Hoshyar Zebari has estimated that Isis has 12,000 fighters in Syria and Iraq. However, the Iraqi government is believed to have about 930,000 security personnel under its command, spread across the army, police force and intelligence services.
There is no doubt that al-Qaeda is a massive threat to security in Iraq. Foreign Minister Hoshyar Zebari has estimated that ISIS has 12,000 fighters in Syria and Iraq.
Mr Maliki has overcome similar challenges to his authority before. In 2008, he launched an operation that saw four army divisions sent to Basra to seize control of the southern city from Shia militias. He then imposed state control over the Baghdad suburb of Sadr City, which had been run by the Mehdi Army of the radical Shia cleric Moqtada Sadr.
However, the Iraqi government is believed to have about 930,000 security personnel under its command, spread across the army, police force and intelligence services.
In 2004, before Mr Maliki came to power, US troops fought two major battles with Sunni militants for control of Fallujah, which saw some of the bloodiest combat Americans had faced since Vietnam.
Mr Maliki has overcome similar challenges to his authority before. In 2008, he launched an operation that saw four army divisions sent to Basra to seize control of the southern city from Shia militias.
He then imposed state control over the Baghdad suburb of Sadr City, which had been run by the Mehdi Army of the radical Shia cleric Moqtada Sadr.
US Secretary of State John Kerry said that while Washington will help Iraq against the militants, it was a "fight that belongs to the Iraqis", and that US soldiers would not return.
In 2004 US troops fought two major battles with Sunni militants for control of Fallujah, which saw some of the bloodiest combat Americans had faced since Vietnam.
