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BAGHDAD (Reuters) - Iraqi forces made fresh gains on Wednesday in an offensive to dislodge Islamic State from the city of Tal Afar, a militant stronghold in the northwest of the country, the military said.

On the fourth day of the offensive, Iraqi units seized two neighborhoods on the western outskirts of the city, al-Kifah north and south, according to statements from the Iraqi joint operations command.

On Tuesday, army and counter-terrorism units broke into Tal Afar from the east and south.

The city is the latest objective in the U.S.-backed war on Islamic State, following the recapture of Mosul after a nine-month campaign that left much of the city in ruins.

The fall of Mosul effectively marked the end of the self-proclaimed caliphate Islamic State declared over parts of Syria and Iraq in 2014.

About three quarters of Tal Afar remains under militant control including the Ottoman-era citadel at its centre, according to an operational map published by the Iraqi military.

Located 80 km (50 miles) west of Mosul, Tal Afar lies along the supply route between Mosul and Syria. It has produced some of IS’s most senior commanders and was cut off from the rest of IS-held territory in June.

Up to 2,000 battle-hardened militants remain in Tal Afar, according to U.S. and Iraqi military commanders.