Iraqi forces have recaptured more than a third of eastern Mosul four weeks into the battle to retake the city from the Islamic State group, the interior ministry's spokesman said Tuesday.

"More than half of this (eastern) side has been liberated," Saad Maan said at a televised news conference.

Iraqi forces launched the massive operation to retake Mosul, the last IS-held Iraqi city, on October 17, advancing towards it from the north, east and south.

Forces on the eastern front were the first to reach Mosul, and Iraq's elite Counter-Terrorism Service has since recaptured several areas inside the city.

On the southern front, interior ministry forces are approaching Mosul airport on the city's southern outskirts.

IS overran large areas north and west of Baghdad in 2014, but Iraqi forces backed by US-led air strikes have since regained much of the territory lost to the jihadists.

In addition to Mosul, IS holds the town of Tal Afar to its west, and also still controls areas in the western province of Anbar.