The United States is "committed" to supporting Iraq as it battles extremist militants who have seized a swathe of the country’s north.

The United States is "committed" to supporting Iraq as it battles extremist militants who have seized a swathe of the country's north, Secretary of State John Kerry told his Iraqi counterpart Saturday.

U.S. President Barack Obama said he was "looking at all the options" to halt the offensive that has brought the militants within 50 miles (80 kilometers) of Baghdad's city limits, but ruled out any return of US combat troops.

However, a US carrier group was ordered into Gulf waters on Saturday.

During a phone call with Iraqi Foreign Minister Hoshyar Zebari, Kerry stressed that the United States was "committed to supporting Iraq," a State Department statement said.

Assistance from the United States would only be successful if Iraqi leaders were willing to put aside differences and implement a coordinated and effective approach to forge the national unity necessary to move the country forward and confront the threat of ISIL (the so-called Islamic State in Iraq and the Levant)," it added.

Kerry urged the Iraqi government to ratify election results "without delay," form a new government on time and to respect the rights of all its citizens from various religious and ethnic backgrounds.

"The secretary assured the foreign minister that the United States was reaching out to the international community and Iraq's regional neighbors to emphasize the threat that Iraq and the region are under from ISIL and the importance of coming to Iraq's aid at this critical juncture," the State Department said.

Obama has been under mounting fire from his Republican opponents over the swift collapse of Iraq's security forces, which Washington spent billions of dollars training and equipping before pulling out its own troops in 2011.