Iraqi forces say they have surrounded an oil refinery after launching a push to retake the Islamic State-held town of Qayara, south of Mosul.

Special forces spokesman Sabah al-Numan says troops are still fighting a small group of IS militants inside the complex.

Iraqi forces are conducting a series of small-scale operations around Mosul ahead of an eventual push to retake the country's second largest city, which fell to IS in the summer of 2014.

Prime Minister Haider al-Abadi has pledged to drive IS out of the city this year.

Last month Iraqi forces backed by U.S.-led airstrikes retook the Qayara airfield, a transport hub that could prove crucial for an advance on Mosul. Seventy kilometers (40 miles) of territory dotted with militant-held villages lie between Qayara and Mosul.