Iranian paramilitary leader is in Baghdad, aiding Iraq's government

BAGHDAD - U.S. Secretary of Defense Chuck Hagel has ordered an aircraft carrier and two other warships to the Persian Gulf as militants in Iraq have taken control of large sections of the northwestern part of the country.

Hagel says the ships, including the carrier USS George H.W. Bush, will give President Obama added flexibility in protecting American interests there.

Meanwhile, Iraq's prime minister, Nouri al Maliki is rallying Shiite supporters to fight the Sunni insurgents.

And Iraqi troops and Shiite militia fighters apparently slowed down the militants' progress today.

In Baghdad's Shiite enclave of Sadr City, men answered the call to fight jihad, taking up arms against the Sunni enemy, ISIS, which now control two of Iraq's main cities.

The insurgents have threatened to take the capital as well and today security forces in Baghdad were on high alert.

Thousands have poured into recruitment centers in Shiite strongholds across the country and they're not alone.

CBS News can confirm that the head of Iran's paramilitary Quds force, Qassem Suleimani, is here in Baghdad along with Iranian fighters who are helping the Shiite government coordinate its response.

The complete collapse of the Iraqi army in the north of the country has become a scandal here. Tens of thousands have abandoned their weapons and run away. On Saturday, Iraq's prime minister warned there would be consequences for deserting.

Those who failed to carry out their duties or who abandoned their positions, Maliki said, will stand trial and will face severe legal measures.

But for Iraqi soldiers who are captured by ISIS the punishment is far worse. This video appears to show Iraqi special forces being interrogated by Sunni militants.

The soldiers are denounced as unbelievers and shot one by one in the back of the head.

Yet the stunning success of ISIS in the past few days has been celebrated by many Sunnis in Iraq. This country's sectarian fault lines have never been deeper.

The battle for Iraq pits two branches of Islam against each other - Sunni versus Shia.

The attacking militant force, the Islamic State of Iraq and Syria or ISIS for short, is made up of Sunnis. They are the majority branch of Islam overall, but the minority in Iraq.

The democratically elected government of Iraq, which the United States supports, is dominated by Shia, which is also the dominant religion in the bordering country of Iran.

• Iraq jihadists move swiftly, but further gains may not be so easy
• Iraqi cleric calls on Shiites to grab a gun to take on Sunni militants

This week ISIS has taken both Mosul and Tikrit. What might be next?

ISIS appears to be moving south toward Baghdad but the current focus is the city of Samarra, which they have reportedly almost surrounded. This is home to one of the holiest Shiite shrines. When Iraq was consumed by sectarian bloodletting in 2006 it was triggered by an attack on that very same Samarra shrine.