Islamic State jihadist fighters seized two small oilfields in northern Iraq on Saturday after a fierce battle with Kurdish peshmerga forces, Kurdish officials said.

The jihadist attack launched late Friday on the Zumar area, northwest of Mosul, Iraq's second city, drew Kurdish forces deeper into a conflict which has raged for close to two months.

The jihadists "attacked a peshmerga post in Zumar and a fierce battle erupted," said an official in the Patriotic Union of Kurdistan (PUK), one of Iraq's two main Kurdish parties.

He told AFP that 14 peshmerga fighters were killed, a toll confirmed by a senior officer in the Kurdish force.

Another two peshmerga died in fighting around a nearby border crossing with Syria.

The PUK official said the peshmerga killed "around 100" IS fighters and captured 38.

The officials said the peshmerga fought off the jihadists, only to withdraw later on Saturday, allowing IS fighters to take control of the area, which includes the Ain Zalah and Batma fields.

"The two oilfields are now under IS control," an official with the North Oil Co told AFP, adding the fields have a combined capacity of 20,000 barrels per day.

He said the site also includes a small power plant.

"Zumar and the surrounding region fell to Daash, after they pulled out today," Gayath Surchi, another PUK official, told reporters, using the former Arabic acronym for the jihadists.

IS fighters, who run large swathes of neighbouring Syria, launched a blistering offensive on June 9 that saw them capture Mosul and move into much of Iraq's Sunni heartland.

Government forces retreated in the face of the onslaught, with peshmerga troops filling the vacuum and seizing long-coveted areas disputed by the Kurds and Baghdad, including the oilfields.

The peshmerga are widely perceived as Iraq's best organised and most efficient military force but the autonomous Kurdish region in the north has been cash-strapped and its troops stretched.

- US-Kurdish deal? -

According to a senior official, a Kurdish delegation is currently in the United States to demand military support.

"There is US pressure on the Kurdish administration encouraging them to fight the terrorists," Kurdish commentator Aref Qarbani said.

"In return, the US administration would give them guarantees to equip peshmerga forces and acknowledge the new Kurdish reality on the ground," he said.

Iraq's Kurdistan region has expanded by around 40 percent on the back of the chaos caused by the IS offensive.

In equally intense overnight fighting on the main front south of Baghdad, at least 23 pro-government forces were killed by relentless mortar shelling of their positions in Jurf al-Sakhr.

IS militants began attacking the town late Friday, killing 11 soldiers and 12 members of the Asaib Ahl al-Haq militia, an officer and army medic said.

Another seven soldiers were wounded during a subsequent government operation against jihadist fighters in Jurf al-Sakhr, Al-Hamya and Latifiya, the sources said, reporting 37 IS fighters killed.

Using the western city of Fallujah as a rear base, jihadists have repeatedly attacked Jurf al-Sakhr, where pro-government forces want to prevent a foray that would expose the nearby holy Shiite city of Karbala and further encircle Baghdad.

In other attacks on Saturday, five would-be volunteer fighters were killed and 16 wounded in a suicide car bomb attack on a Shiite militia recruitment centre in Balad, north of Baghdad, police said.

Further north in Samarra, a Sunni-dominated city with a heavy militia presence protecting one of the holiest sites in Shiite Islam, two policemen were killed in a roadside bomb blast, police and medical sources said.

And further up the same main northbound road, in the town of Daquq, an air raid designed to head off an IS attack resulted in the deaths of six civilians, a top health official said.

The UN envoy in Iraq, Nickolay Mladenov, expressed concern on Friday over the high number of civilians being killed in Iraq's conflict.

According to the United Nations, 1,186 civilians were among 1,737 people who died in violence across the country in July.