A U.S. aircraft carrier was ordered to move into the Persian Gulf on Saturday as the United State laid out specific ways for Iraq to show it is forging the national unity necessary to gain assistance in its fight against Islamic insurgents.

U.S. Defence Secretary Chuck Hagel ordered the USS George H.W. Bush from the northern Arabian Sea as U.S. President Barack Obama considered possible military options for Iraq. Hagel's press secretary, Rear Adm. John Kirby, said the move will give Obama additional flexibility if military action were required to protect American citizens and interests in Iraq.

Accompanying the carrier will be the guided-missile cruiser USS Philippine Sea and the guided-missile destroyer USS Truxtun. The ships, which carried Tomahawk missiles that could reach Iraq, were expected to complete their move into the Persian Gulf by the end of the day. The Bush's fighter jets also could easily reach to Iraq.

Islamic militants of the Islamic State of Iraq and Syria, or ISIS, have captured large swaths of territory north of Baghdad. Their advance on the capital was sending food prices dramatically higher and prompting tighter security in the city of seven million people.

In a phone call Saturday with Iraqi Foreign Minister Hoshyar Zebari, U.S. Secretary of State John Kerry said U.S. assistance "would only be successful if Iraqi leaders were willing to put aside differences and implement a co-ordinated and effective approach to forge the national unity necessary to move the country forward and confront the threat of [ISIS]," according to a statement by the State Department.

Kerry pointed to the importance of the Iraqi government ratifying election results without delay, adhering to its constitutionally mandated timeframe for forming a new government, and respecting the rights of all citizens as it fights against terrorism, the State Department said.

The aircraft carrier USS George H.W. Bush is seen two days ago as sailors assemble in formation on the flight deck in honour of former U.S. President George H.W. Bush's birthday. (Lt. Juan David Guerra/U.S. Navy)

Amid sectarian strife between Sunni and Shiite citizens, Prime Minister Nouri al-Maliki called for unity of all Iraqis. A Shiite, al-Maliki is widely resented by Sunnis for his perceived sectarian policies.

Kerry told Zebari that the U.S. was emphasizing with the international community as well as those in the region the threat posed by ISIS and the importance of coming to the aid of Iraq.

Airstrike kills Kurdish forces

Meanwhile on Saturday, at least seven members of the Kurdish security forces were killed in an airstrike in Iraq's northeastern province of Diyala on Saturday, police said.

The secretary general of the Kurdish security forces said however that only two people had died near the town of Jalawla in what he described as shelling, and that it was not yet clear whether Iraqi forces or militants were responsible.

The incident and divergent accounts show the potential for security in Iraq to deteriorate further, given the deployment of several heavily armed factions and shifting areas of control.

Members of Iraqi security forces and tribal fighters take part in an intensive security deployment on the outskirts of Diyala province on June 13. (Reuters) Both Iraqi and Kurdish sources said insurgents from the ISIS were also present in the area.

The rapid seizure of Mosul, one of Iraq's largest cities, by insurgents led by ISIS, and the Kurds' takeover of the oil-rich city of Kirkuk this week have raised concerns internationally about the split of the country, as government forces have abandoned their posts.

The Iraqi rapid response units said in a statement that some Kurdish peshmerga forces had behaved in a "strange way," confronting fellow Kurdish tribesmen who were assisting federal government forces in their fight against ISIS.

Jabbar Yawar, the secretary general of the peshmerga, said talks with Iraqi authorities were under way to ascertain what had happened.

Military moves to reclaim Tikrit

Insurgents seized the small town of Adeim in Diyala province after Iraqi security forces pulled out, said the head of the municipal council, Mohammed Dhifan. Adeim is about 100 kilometres north of Baghdad. There was no official confirmation of the loss of the town.

Jawad al-Bolani, a lawmaker and former Cabinet minister close to al-Maliki, meanwhile, said a military offensive was underway Saturday to drive the insurgents from Tikrit, Saddam's hometown north of Baghdad, although fighting in the area could not be confirmed.

Different translations for ISIS: The name in the original is the Islamic State of Iraq and "al-Sham" — an Arabic word that refers to Greater Syria or the Levant. So it is alternately referred to as the Islamic State of Iraq and the Levant, or ISIS or the Islamic State of Iraq and Syria, or ISIS; or other versions of "al-Sham." — The Associated Press

The fast-moving rebellion has emerged as the biggest threat to Iraq's stability since even before the Americans left.

Long-simmering Sunni-Shia tensions boiled over after the U.S.-led invasion ousted Saddam in 2003, leading to vicious fighting between the two Muslim sects. But the bloodshed ebbed in 2008 after a so-called U.S. surge, a revolt by moderate Sunnis against al-Qaeda in Iraq and a Shia militia ceasefire.

The latest bout of fighting, stoked by the civil war in neighbouring Syria, has pushed the nation even closer to a precipice that could partition it into Sunni, Shia and Kurdish zones.