Iraqi forces led by federal police units retook two villages south of Mosul as part of a fresh push on the city's west bank Sunday, a top commander said.

Army Staff Lieutenant General Abdulamir Yarallah said in a statement that forces advancing toward Mosul airport retook Athbah and Al-Lazzagah, reviving a four-month-old offensive that was paused following the reconquest last month of the city's east bank.

The southern front in the Mosul offensive had remained largely stagnant for weeks as the forces deployed there waited for the completion of operations on the city's east bank.

The two villages and neighbouring areas that federal police and the interior ministry's elite Rapid Response forces retook on Sunday are the last before Mosul airport.

The airport and a nearby military base mark the southern approach to Mosul, on the east bank of the Tigris River that divides the city.

Elite fighting units are expected to attempt a foray into the city's western side in the coming days.

Forces battling IS in Iraq's Mosul theatre
Baghdad (AFP) Feb 19, 2017 - A wide array of Iraqi and international forces are involved in the operation to retake Mosul from the Islamic State group, which overran the country's second city in 2014.

The eastern side of the city has now been retaken and, four months into the offensive on Mosul, Iraq announced Sunday that its forces were launching an assault on the west bank.

These are the main forces battling the jihadists in and around Mosul:

- Counter-Terrorism Service -

The CTS is an elite Iraqi special forces unit that has spearheaded assaults in most key battles against IS. It did most of the fighting in east Mosul and is expected to enter west Mosul in the coming days.

Baghdad has not divulged casualty figures but the country's best-trained and most seasoned force is believed to have suffered heavy losses.

- Rapid Response Division -

The CTS's interior ministry counterpart that has developed into a key assault force in Iraq's war against IS. It has advanced on Mosul from the south and is a key component of the new phase of the operation announced Sunday and focused on Mosul airport.

- Army -

The army has begun playing an enhanced role in operations against the jihadists since it was revitalised by US-led training after several of its divisions collapsed during the IS offensive two years ago.

It struggled however when it entered east Mosul and needed the support of special forces. It is active on all four sides of Mosul and is acting as a holding force in reconquered east Mosul.

- Police -

Includes paramilitary federal police and provincial police forces. Many Iraqi police forces have played roles more akin to those of soldiers in the war against IS.

The federal police force has been mostly active on the southern front and is involved in the new phase of operations announced on Sunday.

- Hashed al-Shaabi -

An umbrella organisation created in 2014, which includes a dizzying collection of paramilitary forces who vary in skill and in the degree to which they are actually under government control.

The main groups are Iranian-backed Shiite militias, including Ketaeb Hezbollah, Asaib Ahl al-Haq and Badr. The Hashed played a major role in the anti-IS fight in Iraq but forces within it have also carried out abuses.

It also includes Sunni tribal forces sometimes referred to as "tribal mobilisation" or "national mobilisation" that have supported operations on the edges of Mosul and in some Christian areas southeast of the city.

The Hashed's main focus since the start of the offensive has been the town of Tal Afar, west of Mosul. They have retaken swathes of desert around it and cut off IS supply lines to Syria.

- Kurdish forces -

The peshmerga are the armed forces of Iraq's autonomous Kurdish region. They nominally answer to the federal government but in practice operate independently, battling IS along a long front in the country's north.

Kurdish forces operated north and east of Mosul but their involvement in the fighting was over in a few weeks and they are not expected to enter the city proper.

- US-led coalition -

A US-led international alliance is carrying out air strikes against IS in Iraq and Syria, and providing training, arms and equipment to forces opposing the jihadists.

There are thousands of coalition military personnel deployed in Iraq, over half of them from the United States. They have trained more than 65,000 members of the Iraqi security forces.

Most are in advisory or training roles, but special forces soldiers who have fought the jihadists on the ground have been deployed and coalition forces near Mosul have also targeted IS with artillery.

- Iranian advisers -

Iranian forces have provided advice and other assistance, including funding for various militias fighting IS in Iraq.

Qassem Soleimani, the commander of Iran's Revolutionary Guards foreign operations wing, has been repeatedly pictured in Iraq during the war.

- Turkish troops -

Deployed at a base near Mosul from which they have carried out artillery strikes against IS. Turkish troops are also present inside Iraq's autonomous Kurdish region.

The federal government has demanded their withdrawal. Turkey has so far declined to do so but its troops have not been drawn deeper into the Mosul offensive, as had been feared.