By Stephen Kalin and Isabel Coles

ERBIL, Iraq (Reuters) - Iraqi forces have retaken around 70 percent of eastern Mosul from Islamic State militants and expect to reach the river bisecting the city in the coming days, Iraq's joint operations commander told Reuters.

Lieutenant General Talib Shaghati, who is also head of the elite counter-terrorism service (CTS) spearheading the campaign to retake the northern city, said the cooperation of residents was helping them advance against Islamic State.

In its 12th week, the offensive has gained momentum since Iraqi forces backed by a U.S.-led coalition renewed their push for the city a week ago, clearing several more eastern districts despite fierce resistance.

"Roughly 65-70 percent of the eastern side has been liberated," Shaghati said in an interview late on Wednesday in the Kurdish capital of Erbil. "I think in the coming few days we will see the full liberation of the eastern side".

The western half of the city remains under the full control of Islamic State, which is fighting to hold on to its largest urban stronghold with snipers and suicide car bombs numbering "in the hundreds" according to Shaghati.

The Mosul assault, involving a 100,000-strong ground force of Iraqi government troops, members of the autonomous Kurdish security forces and mainly Shi'ite militiamen, is the most complex battle in Iraq since the U.S.-led invasion in 2003.

The commander of a U.S.-led coalition backing the Iraqi offensive told Reuters on Wednesday that increased momentum was due largely to better coordination among the army and security forces. He said the Iraqis had improved their ability to defend against Islamic State car bombs.

Although vastly outnumbered, the militants have used the urban terrain to their advantage, concealing car bombs in narrow alleys, posting snipers on tall buildings with civilians on lower floors and making tunnels and surface-level passageways between buildings. They have also embedded themselves among the local population.

HUMAN SHIELDS

The presence of large numbers of civilians on the battlefield has restricted Iraqi forces' use of artillery but the cooperation of residents has also helped them target the militants.

"They give us information about the location of the terrorists, their movements and weapons that has helped us pursue them and arrest some and kill others," Shaghati said.

In the run-up to the Mosul offensive, Iraqi officials expressed hope that residents would rise up against Islamic State, accelerating the group's demise in the city. But mass executions seem to have discouraged widespread resistance.

An Iraqi victory in Mosul would probably spell the end for Islamic State's self-styled caliphate, which leader Abu Bakr al-Baghdadi declared 2-1/2 years ago from Mosul's main mosque after the militants overran the city.

But in recent days, the militants have displayed the tactics to which they are likely to resort if they lose the city, killing dozens with bombs in Baghdad and attacking security forces elsewhere.

An attack claimed by Islamic State killed six people on Thursday on the capital's eastern outskirts.

CTS pushed into Mosul from the east in late October and made swift advances but regular army troops tasked with advancing from the north and south made slower progress and the operation stalled for several weeks.

The roughly 10,000 members of CTS, established a decade ago with support from the U.S. forces, are considered the best-trained and equipped fighters in Iraq.

Shaghati described the role of the international coalition, providing air support and advising Iraqi forces on the ground as "outstanding" and said Islamic State was crumbling under pressure.

"Daesh (Islamic State) devised many plans to obstruct and block us but they failed. We were able to surpass them and these areas were liberated with high speed," Shaghati said.

"We have intelligence that (Islamic State) leaders and their families are fleeing outside Iraq."

(Writing by Isabel Coles; Editing by Janet Lawrence)