baghdad police
Iraqi policemen climb onto a roof of a military base in Baghdad as Jihadists sweep south towards the capital AFP

Iran's elite Revolutionary Guards have been deployed to Iraq, to help government troops defend the capital city of Baghdad from the escalating threat of ISIS insurgents, Iranian security sources have confirmed.

Sunni militant group ISIS, the Islamic State of Iraq and al-Shams, has already seized several areas in the northern part of the country.

The militant group took control of Saddam Hussein's hometown of Tikrit on Wednesday (June 11), but Revolutionary Guard and Iraqi troops overtook 85 percent of the city on Thursday (June 12). ISIS militants seized Mosul, Iraq's second-largest city, earlier this week.

Government forces have so far managed to stall the militants' remarkably rapid advance near Samarra - a city 110km (68 miles) north of Baghdad - and are now bombing insurgent positions in and around Mosul.

Security in Baghdad has been stepped up after a video emerged of the militants threatening to march on the city.

In the latest offensive, two battalions of the Quds Forces have reportedly made significant progress in their defence of the besieged, Shiite-dominated government of Prime Minister Nouri al-Maliki.

As the crisis in the Middle-East deepens, the Iranian military is also considering shifting troops fighting in Syria, to Iraq if the deployment of the Quds Forces is not sufficient to combat the insurgents.

Iran's chief of police, Esmail Ahmadi-Moghaddam, said the National Security Council would consider intervening in Iraq to "protect Shiite shrines and cities."

The Iraqi government has turned to the U.S for military support and authorised airstrikes against insurgents in the looming battle for Baghdad.

President Obama responded saying he would not rule out U.S. air strikes against the insurgents and that his government is looking at "all options", including military action, to help Iraq fight Islamist militants.

He said the United States has an interest in making sure jihadists do not gain a foothold in Iraq.

Meanwhile, the UK's Foreign Secretary William Hague has said that British military involvement in the region is not an option and Iraq's leadership must deal with the deteriorating military situation. He added, however that he is considering humanitarian support.

During an appearance on state television Iranian President Hassan Rouhani called ISIS "an extremist, terrorist group that is acting savagely",

Attending an emergency meeting of the country's National Security Council about events in Iraq, he said: "We, as the Islamic Republic of Iran, will not tolerate this violence and terrorism….We will fight and battle violence and extremism and terrorism in the region and the world."

Meanwhile, ISIS have vowed that it would soon march on Baghdad. "Our final destination will be Baghdad, the decisive battle will be there."