Kurdish troops retook an oilfield from the "Islamic State" (IS) Saturday, a day after the group seized it, a security official said, estimating that the operation killed 40 IS fighters.

Backed by allied warplanes, which flew 27 airstrikes from Friday to Saturday - reportedly killing an IS chemical weapons expert - the troops launched an attack and drove IS out of the Khubbaz oil complex west of the city of Kirkuk, said Brigadier Sarhad Qader of the regional police.

IS uses revenues from illegal oil sales to fund its activities.

"Peshmerga forces and police cleared the Khubbaz field a little while ago and were able to enter it after surrounding it for hours," Qader said of Saturday's fighting, adding that they also retook eight villages.

IS captured the oilfield Friday, seizing 24 workers. A police colonel said officers had to delay the liberation of the hostages because of fears that IS had rigged the bunker it held them in with explosives.

During the operation, a sniper killed peshmerga Major General Hussein Mansur, according to Colonel Kawa Gharib. An attack elsewhere in Kirkuk province killed Brigadier General Shirko Rauf on Friday. IS fighters had also rigged a nearby house with explosives, killing another peshmerga major and wounding four fighters.

Last June, IS overran southwestern Kirkuk en route to capturing much of Iraq's Sunni Arab heartland north and west of Baghdad. That offensive presented both an opportunity for territorial expansion and an existential threat to the three-province autonomous Kurdish region. Several Iraqi military divisions collapsed in the early days of the offensive, clearing the way for the Kurds to take control of a swath of disputed territory they have long wanted to incorporate into their region over Baghdad's objections.

In mid-January, IS released a group of Yazidis en masse. Earlier in the month, IS let go several Iraqi civilians it had accused of burning the group's flag.

IS vows renewed attacks

Kurds have repeatedly launched assaults on IS, but their recent run of victories has come even before the expected arrival of German forces to train peshmerga fighters. IS has also acknowledged the loss of Syria's town of Kobani, as well as up to 1,000 fighters, but has vowed renewed attacks.

In a video released late Friday, two IS fighters said the airstrikes by the US-led coalition had led to the group's withdrawal from Kobani. One IS fighter vowed to defeat Syrian Kurds People's Protection Units, known as the YPG, calling them "rats."

Even as early as Monday, activists and Kurdish officials said they had nearly cleared Kobani of IS, which had once held nearly half of the town. The group's failure to capture Kobani has proved a major blow to the extremists. IS hopes for an easy victory dissolved into a costly siege under airstrikes by coalition forces and an assault by Kurdish militiamen.

"A while ago we retreated a bit from Ayn al-Islam because of the bombardment and the killing of some brothers," one fighter said, using the Arabic name for Kobani. He spoke with a North African accent.

mkg/shs (Reuters, AFP, dpa, AP)