A coalition of Iraqi and international security forces in Iraq on Sunday began their operation to retake the western side of the city of Mosul from the Islamic State group. Thousands of personnel along with ground and air support have advanced on militant positions in the city, with two villages being captured during the first few hours of the operation, BBC reported.

Announcing the start of the campaign, Iraqi Prime Minister Haider al-Abadi said the security forces “are beginning the liberation of the citizens from the terror of Daes [Islamic State]”. Abadi also asked personnel to “respect human rights” during the campaign, Reuters reported. At least 6,50,000 civilians are believed to be trapped in the city. Islamic State fighters have used civilians as human shields during past battles.

Coalition forces commander Lieutenant General Stephen Townsend said the fight for Mosul “would be a tough one for any army in the world”. Other officials said they expected the battle for the western side of the city to last longer than the eastern one because of rougher terrain as well as narrower passageways, which will make troop and vehicular movement difficult.

The Islamic State group was believed to have over 6,000 fighters when the operation started in October 2016. That number has come down by around 1,000, according to Iraqi estimates. The city, which the Islamic State group has held control of since 2014, is its last major stronghold in the country. The international fraternity has expressed confidence that taken back the control of the region would deal a strong blow to the group’s designs.