Half a dozen units of Islamic State group fighters holed up in western Mosul began their morning radio checks at just after 4 a.m. It was still dark and Iraqi forces deployed a few blocks away were listening in as they prepared an advance on the city's al-Rifai neighborhood.

"Thirty, what's new? ... 120, do you read me? What's up?" the IS radio operator said, using Iraqi slang.

About 40 minutes later the first U.S.-led coalition airstrike hit as Iraqi forces pushed across a main road and began clearing the neighborhood's narrow streets.

"We're seeing at least two squirters at the impact site," a member of the coalition force radioed back to the Iraqi troops in Australian-accented English, using a slang term for badly wounded IS fighters. Moments later the extremists were calling for doctors over their own radio network.

Over the next 12 hours, more than 10 coalition airstrikes hit al-Rifai's eastern edge. Most targeted small teams of two or three IS fighters manning sniper rifles or machine guns so Iraq's special forces units could advance on the ground.

Military operations like the one in al-Rifai this week are accelerating in Mosul as part of a drive to retake the handful of districts still under IS control before the holy month of Ramadan begins at the end of May. And despite recent allegations of increased civilian casualties, advances on the ground continue to be backed by heavy airstrikes and artillery.

Launched in mid-February, the fight for Mosul's western sector has been marked by some of the most difficult fighting and catastrophic destruction yet in Iraq's war against IS. The brutality of the operation was highlighted by a single incident just a month into the operation — a U.S. airstrike on March 17 that killed more than 100 people sheltering in a home, according to residents and other witnesses interviewed by The Associated Press.

By contrast, Mosul's eastern half was retaken in 100 days of fighting. While front lines stalled at times, the area was less densely populated, neighborhoods were more modern with wider streets allowing tanks and other armored vehicles greater freedom of movement and the area was never under siege, allowing many IS fighters to flee westward.

The number of civilians reportedly killed in coalition airstrikes in Iraq and Syria spiked to 1,800 in March, more than three times the number reported a month earlier, according to Airwars, a London-based group that tracks civilian deaths from coalition airstrikes. Official figures from the Pentagon, which is slower in confirming deaths, are far lower: It said last month that it has confirmed coalition airstrikes killed at least 352 civilians in Iraq and Syria combined since the campaign against IS started in 2014.

The March 17 incident sparked outrage in Iraq and beyond. The U.N. called on Iraq to conduct "an urgent review of tactics to ensure that the impact on civilians is reduced to an absolute minimum."

The Pentagon is still investigating the incident but Gen. Joseph Votel, head of U.S. Central Command, said the munitions used by the U.S. that day should not have taken the entire building down, suggesting that militants may have deliberately gathered civilians there and planted other explosives.

An Iraqi officer overseeing the Mosul operation said that after the March 17 strike, he received orders to no longer target buildings with munitions. Instead airstrikes were directed to the streets and gardens beside IS locations. But the order lasted only a few days. Now, as Iraq's army, special forces and militarized federal police push to clear the last vestiges of western Mosul held by IS, the volume of airstrikes is the same as when the mission to retake western Mosul first began, said the officer, who spoke on condition of anonymity in line with regulations.

A few blocks from the front-line advance, Faisa Muhammed, her children and grandchildren huddled Tuesday on the ground floor of their home. Car bombs, airstrikes and mortar attacks had already broken every window in their house. Their street had been declared liberated the day before but the fight was still so close that the force of nearby explosions filled their living room with dust and blew open the curtains they had pulled closed over the shattered window frames.

Muhammed said two airstrikes hit on either side of her home over the past week. One killed a single IS fighter in a neighboring garden and another killed a three-member sniper team on the roof of another house.

"If we hear only 10 explosions in a day, that's very little," she said as her grandchildren sat quietly even as the walls around them shook. When the whine of a mortar sounded overhead everyone mechanically plugged their ears with their fingers. Soldiers took cover in her garden when a nearby airstrike sent rubble raining down on the street outside.

"This has become normal for the children," Muhammed said.

Just over eight square kilometers (three square miles) of western Mosul remains under IS control, but within that area is the Old City — congested, densely populated terrain that is expected to present some of the most difficult fighting and greatest danger to civilians.

The renewed push to drive IS out of the remaining pockets still under its control was launched just over two weeks ago and since then Iraqi forces have retaken more than 30 square kilometers (12 square miles), according to the U.S.-led coalition, forcing thousands to flee. Some 500,000 people have fled western Mosul since February and the United Nations warned another 200,000 may be forced to flee as the operation continues.

U.N. humanitarian coordinator Lise Grande called the numbers "overwhelming."

Iraqi special forces Lt. Gen. Abdul-Wahab al-Saadi said he hopes to complete the Mosul operation before Ramadan begins around May 27 in order to get resources to the hundreds of thousands of civilians believed to be besieged in IS-held Mosul.

"It is very important to reach them very quickly," he said, adding that a victory before the holy month would "bring joy to the residents of Mosul and the troops."


Associated Press writers Sinan Salaheddin in Baghdad and Mouhammad Nouman in Mosul, Iraq, contributed to this report.