MOSUL, Iraq, Jan. 10 (Xinhua) — Iraqi security forces on Tuesday advanced further inside the eastern side of the Islamic State stronghold in the city of Mosul in northern Iraq, as fierce clashes continued against the extremist militants, the Iraqi military said.

In the eastern front, the elite forces of Iraq's Counter-Terrorism Service (CTS) completely freed the neighborhood of Sukkar and made significant progress in the adjacent neighborhood of Siddeeq, amid fierce clashes with the extremist militants, a statement by the Iraqi Joint Operations Command said.

The battles in the two neighborhoods left some 20 militants killed and a booby-trapped car destroyed, the statement said.

Meanwhile, the CTS commandos freed al-Dhubbat neighborhood and took part of the adjacent neighborhood of al-Maliyah, leaving dozens of IS militants killed and two of their car bombs destroyed, the source said.

Several governmental offices were recaptured during Tuesday's advance, including communication complex, provincial electricity department and a security headquarters, the source added.

The latest CTS advance pushed the IS militants to blow up sections of two bridges to prevent the government forces from launching operations to retake the western side of Mosul across the Tigris, according to the statement.

Mosul's five bridges across the Tigris had already been partially damaged by the U.S.-led coalition airstrikes to slow the movement of the IS militants between the two sides of the city.

In the southeastern front, the Iraqi federal police and army soldiers pushed further into the neighborhoods of al-Salam, Palestine, Sumer, Yarimja and Sahiron amid heavy fighting with IS militants, leaving dozens of IS militants killed and destroying two vehicles carrying heavy machine guns, the statement said.

In the northern front, the army soldiers backed by international aircraft started in the morning their advance into the neighborhood of al-Hadbaa despite stiff resistance by the extremist militants, while the troops managed to retake control of the northern part of the adjacent neighborhood of Sabaa Nisan, leaving some 25 militants killed and five booby-trapped vehicles destroyed, it added.

The battles in Mosul came as the CTS commandos, army troops and federal police launched on Dec. 29 the second phase of a major offensive to free Mosul.

The troops made their new push into several neighborhoods in the eastern side of Mosul, locally known as the left bank of the Tigris River.

Last month, battles in Mosul had been slowed as extremist militants used locals as human shields, resorted to suicide car bombs and made mortar and sniper attacks in stiff resistance.

The UN High Commissioner for Refugees (UNHCR) said in a recent report that the military operations in Mosul, have pushed about 136,000 civilians to flee their homes in the city and its adjacent districts since the beginning of military offensive in October to reclaim the IS largest stronghold in Iraq.

More than 1.5 million people were trapped in the city of roughly two million population previously. Cold winter worsened the conditions for the displaced people who suffered severe shortages of food and water, while camps and other emergency shelters reached maximum capacity.

Iraqi Prime Minister Haider al-Abadi on Oct. 17 announced a major offensive to retake Mosul, the country's second largest city.

Since then, Iraqi security forces, backed by international coalition forces, have inched to the eastern fringes of Mosul and made progress on other routes around the city.

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