Iraqi security forces on Saturday pushed further toward the old city center of the western side of Mosul amid fierce clashes with Islamic State (IS) militants, the Iraqi military said.

The federal police and interior ministry special forces, known as Rapid Response, advanced in the neighborhood of Bab al-Toub in Mosul city center, fighting heavy clashes against IS militants in the narrow streets of the old neighborhood, said Lt. Gen. Abdul-Amir Yarallah from the Joint Operations Command in a statement.

The troops killed many IS militants and destroyed three car bombs and 20 explosive devices during the battles in Bab al-Toub, the statement said.

The commandos of the Counter-Terrorism Service (CTS) continued their advance inside the neighborhoods of Aghawat and Risala in the west of the old city center, while more CTS troops initiates new advances in the nearby neighborhoods of New Mosul, Nafet and Nablus, leaving many IS militants killed along with destroying five booby-trapped cars and 14 explosive devices, the statement added.

Also in the day, the army's 16th infantry division made a new progress in northwest of Mosul's western side, and the troops recaptured two villages, a compound of industry installation and the major water facility, which provides the western side of Mosul with water, the statement said.

The troops killed many IS militants and destroyed three car bombs and 15 bombs, along with destroying a vehicle carrying IS militants, it added.

Near Mosul, the army's 9th armored Division and the Shiite paramilitary Hashd Shaabi unit seized part of the town of Badush and surrounded the nearby cement plant in northwest of Mosul, according to the statement.

The troops have been fighting heavy clashes in Badush during the past few days, as the the troops managed on Wednesday to recapture Badush prison, the statement said.

The troops also found two mass graves near Badush prison for people said to be killed by IS militants without giving details about the number of the victims.

However, the Hashd Shaabi units announced earlier in the day they had discovered a mass grave at Badush prison containing the remains of hundreds of people executed by the extremist group.

The presence of armored division and the Hashd Shaabi is aimed at surrounding Mosul from the west to cut off the escape route from Mosul and the neighboring Syria.

Iraqi Prime Minister Haider al-Abadi, who is also the commander-in-chief of the armed forces, announced the start of an offensive on Feb. 19 to drive extremist militants out of the western side of Mosul.

Late in January, Abadi declared the liberation of the eastern side of Mosul, or the left bank of Tigris, after more than 100 days of fighting against IS militants.

However, the western part of Mosul, with its narrow streets and a population of between 750,000 and 800,000, appears to be a bigger challenge to the Iraqi forces.

Mosul, 400 km north of the Iraqi capital of Baghdad, has been under IS control since June 2014, when government forces abandoned their weapons and fled, enabling IS militants to take control of parts of Iraq's northern and western regions.

Source: Xinhua