Jihadists were pushing toward Baghdad on Thursday after capturing a town just hours to the north, as the US mulled air strikes in a bid to bolster Iraq's collapsing security forces.
Fighters from the Sunni Muslim Islamic State of Iraq and the Levant (ISIL) have spearheaded a major offensive that began late Monday, overrunning the northern province of Nineveh and significant parts of Kirkuk to its southeast and Salaheddin to its south.
This morning they were advancing on Baghdad, after seizing the town of Dhuluiyah just 90 kilometres away, witnesses and officials said, adding that the nearby Muatassam area has also fallen.
ISIL spokesman Abu Mohammed al-Adnani promised the group would drive on to Baghdad and Karbala, a city southwest of the capital that is one of the holiest sites for Shiite Muslims, in a statement carried by jihadists' websites.
With militants closing in, Iraq's parliament was to meet in emergency session on Thursday to consider a request from Prime Minister Nuri al-Maliki and the president's office to declare a state of emergency.
Doing so requires a two-thirds vote, making it unlikely to pass the sharply divided parliament, which has produced little significant legislation in years and is often poorly attended.
The swift collapse of Baghdad's control comes on top of the loss of Fallujah, west of Baghdad, at the start of the year. It has been a blow for Western governments that invested lives and money in the invasion that toppled dictator Saddam Hussein in 2003.
Washington is considering several options for offering military assistance to Baghdad, including drone strikes, a US official told AFP on condition of anonymity.
Resorting to such aircraft -- used in Afghanistan, Pakistan and Yemen in a highly controversial programme -- would mark a dramatic shift in the US engagement in Iraq, after the last American troops pulled out in late 2011.
State Department spokeswoman Jen Psaki said the US was committed to "working with the Iraqi government and leaders across Iraq to support a unified approach against ISIL's continued aggression."
But there is no current plan to send US troops back into Iraq, where around 4,500 American soldiers died in the bitter conflict.