The aircraft carrier USS George H. W. Bush will move into the Persian Gulf by Saturday evening, where it will be accompanied by a guided-missile cruiser and destroyer, according to statement by Pentagon press secretary Rear Adm. John Kirby.
"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 statement said.
Meanwhile, Iraqi officials pledged severe punishment for deserting soldiers, whom they blame for the fall of two key provincial capitals earlier this week.
"If soldiers who have left their bases don't rejoin the nearest unit, this will be considered a crime that could merit the death penalty," Prime Minister Nouri al-Maliki said.
On Saturday, insurgents seized the small town of Adeim in Diyala province 60 miles north of Baghdad after Iraqi security forces withdrew. That followed the fall of Mosul and Tikrit this week into the hands of an al-Qaeda splinter group, the Islamic State of Iraq and the Levant (ISIL).
The Sunni group aims to establish an Islamist state spanning Iraq and Syria, where they are also fighting.
About 750,000 men lined up at volunteer centers in Baghdad to answer the call by a top Shiite cleric, Iranian-born Grand Ayatollah Ali al-Sistani, to fight the militants, Iraqi broadcaster Al-Baghdadiyah reported.
Iraqi officials said there was a massive push to roll back the insurgents' gains in Tikrit on Saturday, with the help of Kurdish militias known as Peshmerga, the channel reported. They drove out militants who had taken over an army outpost about 15 miles west of the oil city of Kirkuk — which had been abandoned by deserting Iraqi army troops. The Kurds, who have an autonomous republic in the north, took control of Kirkuk after the Iraqi army withdrew.
U.N. High Commissioner for Human Rights Navi Pillay on Friday expressed extreme alarm at the dramatic deterioration of the situation in Iraq, citing reports of summary executions and extrajudicial killings.
"The full extent of civilian casualties is not yet known," Pillay said. "But reports suggest the number of people killed in recent days may run into the hundreds, and the number of wounded is said to be approaching 1,000."
She said she was deeply disturbed by reports that ISlL fighters, including prisoners they had released from jails in Mosul and provided with arms, have been actively seeking out — and in some cases killing — soldiers, police and others, including civilians, whom they perceive as being associated with the government.
"We have, for example, received reports of the summary executions of Iraqi army soldiers during the capture of Mosul, and of 17 civilians on one particular street in Mosul City on June 11," she added.
U.N. officials also expressed concern at the more than 500,000 refugees who fled towns taken over by ISIL.
Residents in Mosul and Tikrit expressed bitterness over the army's abandonment of residents.
"People in Mosul were not happy with the Iraqi army but they asked for their protection, not for them to leave the city," said Samir Oda of Mosul. "The soldiers were heading towards Kurdistan — not a single one was left in Mosul. Now we are afraid our city will be destroyed by the government trying to attack the terrorists."
Many have questioned how it is possible that such a small fighting force as ISIL could take over key cities protected by the military and threaten the capital. But analysts say it was to be expected.
"The key thing to emphasize is that while on paper the Iraqi security forces are numerically enormously superior to ISIL, in these towns and cities the Iraqi militant security forces are relatively light in number," said Matthew Henman, manager of IHS Jane's Terrorism and Insurgency Center (JTIC), in London. "They are typically a kind of light infantry force, designed for largely static guard duties, rather than any kind of heavy urban combat."
By comparison, he says, that ISIL is a highly trained, highly organized and heavily armed force with experience in guerrilla operations from years of fighting in Iraq and also extensive experience in urban and street fighting against conventional army forces.
In the longer term, ISIL cannot easily hold onto the territory it has captured, analysts say.
"What has subsequently happened is that the security forces have rallied and started to take the fight back to ISIL and to start pushing them back," said Henman. "Because they are capable of engaging with them and defeating them in open combat. ISIL isn't so heavily experienced and armed that it is able to engage in conventional, prolonged combat with conventional security forces."
Still, disaffected Sunnis, Kurdish ambitions, a weak and often corrupt and brutal security force and government could lead to renewed civil war in the worst crisis since U.S. forces withdrew at the end of 2011, analysts say.
Al-Maliki tried to put a positive note on the situation of deserters.
"This is our chance to clean and purge the army from these elements that only want to make gains from being in the army and the police," he said. "They thought that this is the beginning of the end but, in fact, we say that this is the beginning of their end."
