Iraqi forces launched the multi-pronged "second phase" of the battle to retake eastern Mosul from jihadists on Thursday, a top commander said.

Iraqi forces punched into eastern Mosul after the massive operation to recapture the northern city from the Islamic State group was launched on October 17, but progress slowed to a crawl.

"The second phase of liberating the left bank in Mosul was launched, and our forces began advancing toward Al-Quds neighbourhood," Staff Lieutenant General Abdulghani al-Assadi, a senior officer in Iraq's Counter-Terrorism Service, told AFP.

Mosul, now the last Iraqi city in which IS still holds significant territory, is split by the Tigris River, with the east side referred to as the left bank and the west as the right.

"Now our forces clashed with the enemy and there is resistance," he said, adding that forces on the northern and southern fronts were also advancing.

Iraqi forces north and south of Mosul had so far remained outside the city, with the brunt of the fighting inside it being carried out by the CTS.

IS overran large areas north and west of Baghdad in 2014, but Iraqi forces backed by US-led air strikes have since regained much of the territory they lost to the jihadists.

Iraqi Prime Minister Haider al-Abadi had pledged that Mosul would be recaptured by year's end -- a goal that is now out of reach, as operations in western Mosul have yet to begin.

Abadi also said earlier this week that three months were needed to eliminate IS in Iraq.

Air strike disables Mosul's last bridge: residents
Baghdad (AFP) Dec 28, 2016 - An air strike has disabled the last bridge linking eastern and western Mosul, a city Iraqi forces are fighting to retake from jihadists, residents and a provincial official said.

Iraqi forces have advanced into eastern Mosul -- which is divided by the Tigris River -- and have retaken some neighbourhoods on that side of the city, which has been held by the Islamic State group for more than two and a half years.

But the western part of Mosul, the last Iraqi city where IS holds significant territory, remains in the hands of the jihadists.

"Aerial bombing... cut the bridge, and it is not possible to cross it," Mosul resident Abu Ali told AFP.

Abu Ali said he had crossed the river on Wednesday in a boat, now the only way to do so, as other bridges were previously disabled.

Another Mosul resident who did not want to be identified by name said a strike had cut the bridge, as did an official from Nineveh province, of which Mosul is the capital.

"Al-Atiq bridge was targeted by an air strike," making it unuseable, said Hashim Briskani, the deputy head of the Nineveh province security committee.

Briskani said it had been the last bridge connecting east and west Mosul.

Abu Ali and Briskani both said the strike was on Tuesday.

The US-led coalition carrying out air strikes against IS said it had "disabled two bridges" in the Mosul area on Tuesday, and a third the day before.

IS overran large areas north and west of Baghdad in 2014, but Iraqi forces backed by US-led air strikes have since regained much of the territory they lost.