"This is an extremist, terrorist group that is acting savagely," Rouhani said live on state television.

The president did not elaborate on what steps Iran would take to help thwart a bid by fighters from the Islamic State of Iraq and the Levant (ISIL) to push toward Baghdad after seizing several cities and towns to the north.

But he said he would head to a meeting of Iran's Supreme National Security Council immediately after his speech.

That body decides on the Islamic state's major foreign policy and security policies, and it would have to approve any military support Tehran might want to provide to Baghdad.

"For our part, as the government of the Islamic Republic of Iran ... we will combat violence, extremism and terrorism in the region and the world," said an agitated Rouhani.

The president spoke even as the heavily armed militant group on Thursday seized a string of towns near Baghdad after a lightning offensive that began in Nineveh province late on Monday.

Iran is seen as an ally of Iraq's Shiite prime minister, Nuri al-Maliki, whose government's swift loss of control has raised international alarm.

Rouhani meanwhile questioned ISIL's claims to have Islamic roots.

"Unfortunately, they name themselves Muslim and brand their way as jihad, and say they are implementing the way of Koran and Islam," said Rouhani, insisting that the religion's message was one of peace.

On Wednesday, Foreign Minister Mohammad Javad Zarif had condemned the "murder of Iraqi citizens" as he offered Baghdad "support" against terrorism. He too did not elaborate.

ISIL jihadists are also fighting to overthrow Tehran's close ally President Bashar al-Assad in Syria.

Photographer killed covering north Iraq clashes
Kirkuk, Iraq (AFP) June 12, 2014 - A news photographer was killed while covering fighting between Kurdish security forces and jihadists in northern Iraq on Thursday, medical and security sources said.

Kamran Najm Ibrahim died and 14 Kurdish security personnel were wounded in the clashes west of the oil city of Kirkuk, where the militants have seized a string of mainly Sunni Arab towns in the ethnically divided province.

Ibrahim, a well-known freelance photographer, was the first journalist to lose his life covering a major offensive spearheaded by jihadist group the Islamic State of Iraq and the Levant, which began late on Monday.

The militants have overrun a large swathe of northern and north-central Iraq, including second city Mosul.

Iraq is one of the most dangerous countries in the world for journalists, and comes in for frequent criticism from media watchdogs.

Kurdish security forces, known as peshmerga, took control of Kirkuk city on Thursday after soldiers of the Iraqi army quit their posts, officials said.

Kurdish leaders have long laid claim to Kirkuk and a swathe of territory from Iraq's eastern border with Iran to its western border with Syria that they want to incorporate in their autonomous region in the north.

The militant offensive has cleared the way for the Kurds to take control of the disputed areas that Baghdad has long opposed them adding to their autonomous region.

But moving into the disputed areas has put Kurdish forces in the line of fire of the mainly Sunni Arab militants.