BAGHDAD (AFP) - Iraq has received Russian Mi-28 attack helicopters and will use them against militants who have overrun large parts of the country, the defence ministry said on Saturday.

A ministry statement did not specify how many of the heavily armoured two-seat gunships it has received or what it paid for them.

But a video posted on its website showed a hangar containing multiple desert camouflage-painted Mi-28s, which are capable of all-weather and day and night operation.

Militants led by the Islamic State (IS) jihadist group launched a major offensive in June, sweeping Iraqi security forces aside and overrunning most of the country's Sunni heartland.

While the relentless militant advance has since been checked, Iraqi forces are struggling to push them back.

Lacking air support poses a major challenge for Iraqi forces, and Baghdad is seeking to bolster its fledgling helicopter and warplane fleets.

It has already bought Russian Mi-35 helicopters and Su-25 ground attack aircraft, has F-16 warplanes on order from the United States and is seeking American AH-64 Apache attack helicopters as well.