WASHINGTON - Secretary of State John Kerry said on Saturday that the United States was looking at "a range of options" that could help the Iraqi security forces fight against advancing Islamist militants.

In a phone conversation with his Iraqi counterpart Hoshyar Zebari, the top US diplomat reiterated Washington's commitment to supporting Baghdad, saying President Barack Obama "is examining a range of options that could help the Iraqi security forces push back on ISIL advances," the State Department said in a statement.

The Islamic State in Iraq and Levant (ISIL), an offshoot of al-Qaida, was continuing its battle on Saturday against Iraqi security forces in its push on Baghdad, after seizing major cities in northern Iraq in recent days, including Mosul, the second largest city, and Tikrit, the hometown of former Iraqi president Saddam Hussein.

Kerry told Zebari the Obama administration was approaching other countries, including Iraq's neighbors, to urge them to offer help "at this critical juncture."

Obama, in a speech on Friday, set conditions for US assistance including efforts by Baghdad to mend divisions.

The president ruled out sending back US troops, but said he had asked his national security team to prepare "a range of other options" in support of Iraqi security forces, and he would review the options "in the days ahead."

Iraqi Prime Minister Nouri al-Maliki had reportedly asked for American airstrikes against extremist staging areas in his country.

US Defense Secretary Chuck Hagel on Saturday ordered the aircraft carrier USS George H.W. Bush to move from the North Arabian Sea into the Gulf.

The move will give Obama "additional flexibility should military options be required to protect American lives, citizens and interests in Iraq," Pentagon spokesman John Kirby said.

The aircraft carrier will be accompanied by the guided-missile cruiser USS Philippine Sea and the guided-missile destroyer USS Truxtun, and the warships are expected to complete their transit into the Gulf later Saturday evening, he said.