Kurdish Peshmerga forces backed by U.S.-led coalition airstrikes launched a fresh attack on ISIL militants in northern Iraq in the early hours of Sunday, as part of a plan to close in on their de facto capital Mosul,

Kurdish Peshmerga forces backed by U.S.-led coalition airstrikes launched a fresh attack on ISIL militants in northern Iraq in the early hours of Sunday, as part of a plan to close in on their de facto capital Mosul, a Kurdish official said.

The offensive began after heavy shelling and several airstrikes, a Reuters correspondent reported from Wardak, 30 km (19 miles) south-east of Mosul, where some of the Peshmerga forces are deployed. Clouds of black smoke could be seen at a distance, possibly tires or other items set on fire by the militants to obstruct the planes' visibility.

The Iraqi army and the Peshmerga forces of the Kurdish self-rule region are gradually taking up positions around Mosul, 400 km (248 miles) north of Baghdad, from whose Grand Mosque in 2014 ISIL terrorist leader Abu Bakr al-Baghdadi declared a caliphate spanning regions of Iraq and Syria.

Mosul is the largest urban center under the terrorists' control, with a pre-war population of nearly 2 million.

Its fall would mark their effective defeat in Iraq, according to Iraqi Prime Minister Haider al-Abadi, who has said he aims to retake the city this year.

The operation that started Sunday is part of the "shaping operations" to prepare for an offensive on the city itself, said a Kurdish official who declined to be identified.