Fighting erupted at the northern approaches to Baghdad today as Iraq accused Saudi Arabia of backing militants who have seized swathes of territory in an offensive the UN says threatens its very existence.
Washington deployed some 275 military personnel to protect its embassy in Baghdad, the first time it has sent troops to Iraq since it withdrew its forces at the end of 2011 after a bloody and costly intervention launched in 2003.
It was also mulling air strikes against the militants, who are led by the jihadist Islamic State of Iraq and the Levant (ISIL) but also include loyalists of now-executed Sunni Arab dictator Saddam Hussein.
Since the insurgents launched their lightning assault on June 9, they have captured Mosul, a city of two million people, and a big chunk of mainly Sunni Arab territory stretching south towards the capital.
The offensive has displaced hundreds of thousands of people and sent jitters through world oil markets as the militants have advanced ever nearer Baghdad leaving the Shiite-led government in disarray.
Officials said today that militants briefly held parts of the city of Baquba, just 60 kilometres from the capital.
They also took control of most of Tal Afar, a strategic Shiite-majority town between Mosul and the border with Syria, where ISIL also has fighters engaged in that country's three-year-old civil war.
The overnight attack on Baquba, which was pushed back by security forces but left 44 prisoners dead at a police station, marked the closest that fighting has come to the the capital.
In Tal Afar, militants controlled most of the town but pockets of resistance remained.
Soldiers, police and armed residents held on to parts of its airport, the deputy head of the provincial council, Nureddin Qabalan, said.
Further south, security personnel abandoned the Iraqi side of a key crossing on the border with Syria, officers said.
Syrian rebel groups opposed to ISIL, who already controlled the other side of the Al-Qaim crossing, advanced across the border to take over.
The Iraqi army abandoned the Rabia border crossing further north to Kurdish forces last week.
In ethnically mixed Kirkuk province, militants took control of Multaqa village, but were repelled by security forces in Bashir village.
The swift advance of the militants has sparked global alarm, with UN envoy to Baghdad Nickolay Mladenov warning that Iraq's territorial integrity was at stake.
"Right now, it's life-threatening for Iraq but it poses