John Kerry has arrived in Baghdad to discuss the crisis in Iraq with top leaders, as Sunni fighters continued to make gains against government forces in the north of the country.
The US secretary of state is due to meet the Shia prime minister, Nouri al-Maliki on Monday, and Sunni and Kurdish leaders on his visit.
A state department spokesman said Kerry would "discuss US actions under way to assist Iraq as it confronts this threat and urge Iraqi leaders to move forward as quickly as possible with its government formation process to form a government that represents the interests of Iraqis".
Kerry said on Sunday that the US would not pick or choose who rules Baghdad. He said, however, Washington had noted the dissatisfaction among Kurds, Sunnis and some Shia with Maliki's leadership and emphasised that the US wanted Iraqis to "find a leadership that was prepared to be inclusive and share power".
The US government has ruled out sending ground troops to aid the Iraqi government against its fight with the Islamic State of Iraq and its Sunni allies, but has kept an option open to use air power. It has moved a carrier strike group and troops transports into the Gulf area.
The visit comes as Sunni fighters led by the ISIL have expanded their offensive in Iraq, capturing more territory from the government.
ISIL, was reported on Sunday to have taken the towns of Qaim, Rawah and Anah in Anbar province. Qaim, located on the border with Syria, hosts a key crossing between the two countries.
Fighters also claim to be in full control of the northern city of Baiji, which hosts Iraq's biggest oil refinery, though the military denies the rebels control the refinery itself.
The Associated Press news agency, citing Iraqi miltary officials, reported that Sunni fighters captured two border crossings, the Turaibil crossing with Jordan and the al-Walid crossing with Syria, on Sunday.