A government building that was destroyed in clashes is pictured during a battle with Islamic State militants in Mosul, Iraq, March 7, 2017. (Xinhua/Reuters Photo)

MOSUL, Iraq, March 7 (Xinhua) -- Iraqi security forces on Tuesday dislodged Islamic State (IS) militants from some main government buildings in the old city center of western side of Mosul, the Iraqi military said.

The federal police and interior ministry special forces, known as Rapid Response, fought hours of fierce overnight clashes against the extremist militants and managed to free large parts of the neighborhoods of Dawassa and Dandan, recapturing the old government complex, museum, court buildings and Nineveh's provincial police command, Lt. Gen. Abdul-Amir Yarallah, from the Joint Operations Command said in a statement.

In the morning the troops captured the foot of a strategic bridge across the Tigris River, known as al-Hurriyah Bridge and the adjacent municipality building, as well as the building of the central bank, a provincial security source told Xinhua on condition of anonymity

The troops killed many IS militants and clashes are underway to gain more ground and to clear the freed areas and buildings, the source said.

Meanwhile, the commandos of the Counter-Terrorism Service (CTS) continued their fierce clashes against IS militants in the neighborhoods of Mansour and Tel al-Rumman in the southwestern part of Mosul's western side, locally known as the right bank of Tigris River, according to Yarallah.

The battles in southwestern Mosul are part of the push of the CTS special forces deeper toward the central part of Mosul's western side.

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, locally known as the right bank of Tigris River, which bisects the city.

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.