Is Iraq losing control of its biggest province?
Al-Qaeda-linked fighters and Sunni tribes have taken control of key cities in Iraq's large Anbar province. Here is a guide to what's happening.What's going on?
In short, the government lost control of the strategic cities of Ramadi and Falluja, to the west of Baghdad.
In Falluja, 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.
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.But there's always violence, so why is this so important?
Anbar is Iraq's biggest province, has a Sunni Arab majority and borders Syria, Jordan and Saudi Arabia.
It is the first time insurgents have controlled territory in Anbar province since 2004, when they were driven out by US-backed Iraqi troops.
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.
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.
Ramadi and Falluja 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.
Anbar was at the heart of the insurgency which followed the US-invasion of Iraq in 2003 and resistance there has never been extinguished.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, Falluja 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 Falluja 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?
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.
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.