The US Secretary of Defense Chuck Hagel has ordered the aircraft carrier USS George H.W. Bush to move from the North Arabian Sea into the Arabian Gulf.
The Pentagon said the order will provide "the Commander-in Chief additional flexibility should military options be required to protect American lives, citizens and interests in Iraq."
The Bush will be accompanied by the guided-missile cruiser USS
Philippine Sea and the guided-missile destroyer USS Truxtun.
The ships are expected to be in position in the Gulf later tonight.
Earlier, an attack by insurgents that threatened to dismember Iraq seemed to slow today after days of lightning advances .
Government forces regained some territory in counter-attacks, easing pressure on the Shia-led government in Baghdad.
As Iraqi officials spoke of wresting back the initiative against Sunni militants, neighbouring Shia Iran held out the prospect of working with its long time US arch-enemy to help restore security in Iraq.
US President Barack Obama said he was reviewing military options, short of sending combat troops, to combat the insurgency.
The US ordered an aircraft carrier moved into the Gulf today, readying it in case Washington decides to pursue a military option after insurgents overran towns and territories in the north and advanced on Baghdad.
Thousands of people responded to a call by Iraq's most influential Shia cleric to take up arms and defend the country against the insurgency.
In a visit to the city of Samarra, Prime Minister Nourial-Maliki vowed to rout the insurgents, whose onslaught has put the future of Iraq as a unitary state in question and raised the spectre of sectarian conflict.
The militant gains have alarmed both Maliki's Shia supporters in Iran and the US, which helped bring him to power after invading the country and toppling former Sunni dictator Saddam Hussein in 2003.
Oil prices have jumped over fears of exports being disrupted from OPEC member Iraq.
But having encountered little resistance in majority Sunni areas, the militants have now come up against the army.
The army clawed back some towns and territory around Samarra today with the help of Shia militia.
Militants in control of Tikrit, 45km north of Samarra, planted landmines and roadside bombs at the city's entrances.
This was done anticipating a counter-attack by government forces.
Residents said the militants deployed across the city and moved anti-aircraft guns and heavy artillery into position.
Families began to flee north in the direction of Kirkuk, an oil-rich city which Kurdish forces occupied last Thursday after the Iraqi army fled.
USS George H.W. Bussh aircraft carrier