Elite Iraqi troops backed by US jets battled jihadists near Baghdad Wednesday as President Barack Obama insisted US ground troops would not be deployed to battle the Islamic State group.

Obama offered reassuring words to troops at MacDill Air Force Base in Florida, the headquarters of US Central Command, where he met with military commanders to discuss how to defeat the powerful and brutal extremist organisation while keeping America out of another protracted conflict.

"The American forces that have been deployed to Iraq do not and will not have a combat mission," Obama said.

His comments came after America's top military officer suggested that deploying ground forces was a possible future option, sparking hand-wringing in Washington about possible "mission creep".

But expanded air strikes were already turning up the heat on Islamic State fighters.

According to Iraqi military and tribal leaders, US jets struck three IS targets in an area just south of Baghdad dubbed the "triangle of death", killing at least four militants on Tuesday.

Fierce fighting subsequently broke out in the Jurf al-Sakhr area, just a few dozen kilometres (miles) from Baghdad, along the Euphrates river.

Renewed clashes on Wednesday left at least eight soldiers dead, an officer and an army medic said.

The US military did not provide the exact locations of its targets southwest of Baghdad but the latest fighting suggests the strikes are to "soften" IS positions in support of Iraqi army operations.

The Jurf al-Sakhr region is key because it sits on the Euphrates between the major Sunni insurgent bastion of Fallujah, west of Baghdad, and the country's most revered Shiite holy sites south of the capital.

A leader from the local Janabi tribe and an army lieutenant said the push was led by the Golden Brigade, which is widely recognised as the best force in the country.

Critics say it may be the only credible fighting force in what is sometimes derided as "a checkpoint army".

The brigade, which spearheaded an offensive to retake the country's largest dam north of Mosul last month, has been hopping from one key frontline to another.

- 'We will find you' -

Obama, who last week unveiled his strategy to "degrade" and "destroy" the IS group, stood firm on its pledge that a US combat mission was not on the cards -- but insisted the jihadists would be defeated.

"Our reach is long. If you threaten America, you will find no safe haven. We will find you eventually," he said.

He again emphasised the broad-based nature of the coalition to defeat the jihadists, and acknowledged Saudi Arabia for agreeing to host a US mission for training moderate Syrian rebels.

"Australia and Canada will send military advisers to Iraq. German paratroopers will offer training," he said.

British and French planes have already started surveillance missions over Iraq.

The US administration has said its strategy in Iraq would involve helping to revamp an army it had not finished training when the eight-year occupation ended in 2011.

General Martin Dempsey, chairman of the US Joint Chiefs of Staff, said on Tuesday that US military advisers could "provide close-combat advising".

But the White House insisted the idea of US troops in battle was a "purely hypothetical scenario".

The more than 160 air strikes launched by the US since August 8 have achieved some results, apparently forcing top IS leaders to cross the border back into neighbouring Syria.

The Syrian Observatory for Human Rights said Wednesday that nearly 50 people, including seven women and a child, had been killed since Monday in government air strikes on Talbisseh.

On Tuesday, Kurdish peshmerga forces -- which are receiving military equipment from Washington and some of its Western allies -- retook seven Christian villages east of the Iraqi city of Mosul.

The villages had been emptied of their population during an IS offensive in August.

According to a senior Kurdish leader, Roj Nuri Shaways, a top IS military commander known as Abu Abdullah was killed in the fighting.

- Bridge destroyed -

Calls have been mounting in Iraq for Washington to expand its air support to Sunni tribesmen fighting the jihadists, particularly in the town of Dhuluiyah, north of Baghdad.

On Wednesday, a suicide car bomb destroyed a key bridge in Ramadi, a city west of Baghdad where the support of Sunni tribes is seen as vital to any nationwide fightback against the jihadists.

Seven people, mostly civilians, were also killed in the blast.

In Washington, Defence Secretary Chuck Hagel told US lawmakers Tuesday that plans were being laid to hit targets in Syria, where IS is holding Western hostages and has a stronghold in the city of Raqa.

In the past month, IS sparked global outrage by releasing video footage of the beheadings of two US reporters and a British aid worker. It warned it would take the battle to America and its allies.

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