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A crowd of Iraqi officers looked out at the Tigris River Friday from a balcony of Mosul's Nineveh International hotel. Just over three months ago, the men were some 45 kilometers (28 miles) away in a cluster of desert villages on the edge of Nineveh plain.

"Our message to the rest of Mosul's residents is that victory is near," said Lt. Gen. Abdul-Ghani al-Asadi, on a celebratory tour after the city's east was declared largely liberated on Wednesday.

The progress of Iraqi forces, halting at first, sped up this month as they closed in on the river that roughly divides Mosul into eastern and western halves. But that momentum is unlikely to be sustained and the city's western half is poised to be a much tougher fight for the already fatigued forces.

IS DEFENSES

When Sgt. Maj. Hussam Abdul-Latif pushed into Andalus on the morning of Jan. 16, he said the fight for the small neighborhood about a kilometer from the Tigris was nothing like his earlier battles in Mosul. This time, he said most IS fighters here fled hours before his troops arrived.

Safwan Thanoon, an Andalus resident, said dozens of fighters sped off on motorcycles overnight.

"This morning, not a single man was left, just those two corpses," he added, pointing to a mangled body of an IS fighter in the street and another inside the garden of a nearby house.

"If they had stayed here it would have made the battle very difficult," said Abdul-Latif, the special forces officer, explaining how when he first breached Mosul, a handful of snipers holed up within houses and using civilians as shields would slow his convoy, giving dozens of car bombs time to target the stalled forces. The defensive strategy inflicted high casualties and forced long pauses between pushes.

"When we enter the other bank, it will be like the operation beginning all over again," Abdul-Latif said. He expects to face another wave of well-planned defenses and more heavily armed IS fighters.

"COMPLICATED ENVIRONMENT"

Mosul's west is more densely populated and home to the city's oldest neighborhoods. The United Nations estimates some 750,000 people are still in the city's west, many of them residents of outlying villages that IS fighters led on forced marches up the Tigris River valley as they lost ground there.

Narrow, winding streets are also expected to pose a particular problem as Iraqi troops won't be able to largely fight from inside their vehicles like they did in the city's east.

"We don't have a strategy yet for these areas," Maj. Gen. Sami al-Arithi said, referring to the older parts of Mosul. "For now our approach will be to just surround them and wait."

U.S. Army Maj. Gen. Joseph Martin, said Mosul's older districts, some with roads only wide enough for foot traffic, make that part of the city a more "complicated environment."

"West Mosul will be as tough as east Mosul, and from our view even tougher," he said, in a phone interview from the main coalition base in Baghdad's green zone.

MOMENTUM

Retaking the Andalus neighborhood came on the heels of a string of advances in eastern Mosul. Within a few days Iraqi troops retook the city's university, the Nineveh International hotel and more than half dozen eastern neighborhoods.

Maj. Gen. Joseph Martin, the commander of coalition ground forces, credited the swift progress with greater coordination between Iraq's disparate security forces that allowed Iraqi ground troops to push back IS by launching coordinated attacks.

"They're attacking the enemy from multiple directions and the enemy cannot react," he said.

However, Iraqi ground forces largely credit their victories to thinning IS defenses and nighttime raids across front lines aimed at taking out key local militant leadership. Iraq's special forces first began carrying out such raids in Fallujah with close coalition support. In Mosul, as progress stalled, coalition forces moved deeper into the city in part to aid in the nighttime operations, according to an Iraqi officer who spoke on condition of anonymity as he was not authorized to brief the press.

After U.S.-led coalition airstrikes partially destroyed all five bridges spanning the Tigris, the number of car bombs targeting the troops decreased and they became less sophisticated. Iraqi troops began seeing fewer of the heavily armored car bombs that coalition officials likened to vehicles out of the Mad Max movie franchise. IS fighters also began running out of supplies.

As troops pushed closer to the Tigris, special forces Lt. Gen. Abdul-Wahab al-Saadi reported finding fewer and fewer weapons stockpiles left behind in the houses once used by IS fighters as bases, suggesting fighters were running low on munitions.

HUMANITARIAN CONCERNS

But the cordon of Mosul's east that partially accelerated Iraqi gains there also punished the civilian population and threats of a prolonged siege of the city's west are already worrying aid groups.

Mustafa Muahmmad's brother is stuck in western Mosul and every few days he's able to get a phone call or text message from him. His brother told him water and electricity are intermittent and food prices have soared as the wealthiest residents stockpile everything they can.

"They are all just huddled in the basement," said Muhammad of his brother and his young family.

"At the beginning (of the operation) they were afraid for us," he said, "and now we are afraid for them."

Some aid groups have already begun drafting contingency plans to airdrop humanitarian supplies into the city, according to a senior western diplomat present at military planning meetings. The diplomat did not have clearance to brief the press and so spoke on condition of anonymity.

RE-BURYING THEIR DEAD

Like many families who lost loved ones during the Mosul operation, it was too dangerous for Faris Danoon to travel to his neighborhood's graveyard after a mortar attack killed his son Younis

"All the roads were blocked," he said, explaining he was forced to bury the 10-year-old boy in a garden beside his home. "His mother can't bear it, she is just crying all the time," he said.

As security improves in the city, more and more families could be seen exhuming relatives who they had given makeshift burials amid clashes and reburying them in proper cemeteries.

The Nineveh governorate estimates more than 5,000 civilians have been killed and injured inside Mosul since the operation to retake the city began. Hospitals in neighboring Irbil report treating 1,587 civilians, according to data collected by the United Nations. But that number doesn't include civilians who have died inside Mosul or those injured and treated within the city.

Iraqi troops have also experienced similarly high casualty rates; Irbil hospital officials and Iraqi medics working inside Mosul estimate that more than 1,600 Iraqi troops have been injured or killed during the Mosul operation. The number excludes Kurdish forces known as the peshmerga who participated in the initial stages of the fight.

Special forces private Sahil Najim, a 37 year-old from Wasit province in southern Iraq, said in his company alone, more than 30 men have been killed in the last three months.

"This is our duty," Najim said, "so of course it is worth it. But we still feel sorrow, how could you not?"

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Associated Press writers Salar Salim and Mstyslav Chernov in Mosul, Iraq contributed to this report.