EAST OF MOSUL/BAGHDAD: An elite unit of the Iraqi army paused its weeklong advance on Mosul as it approached the city’s eastern edge Tuesday, waiting for other U.S.-backed forces to close in on Daesh’s (ISIS) last major stronghold in Iraq.

On the ninth day of the offensive on Mosul, government forces and allied Kurdish peshmerga fighters are still fighting their way toward the outer limits of the northern city, in the early stages of an assault which could become the biggest military operation in Iraq in over a decade.

The first force to get near to Mosul, advancing to within a couple of kilometers of Iraq’s second largest city, was the elite U.S.-trained Counter Terrorism Service.

CTS troops have moved in from the east, dislodging Daesh from a Christian region that has been empty of residents since the militants took it over in 2014.

The combat ahead is likely to be more difficult and deadly because of the presence of civilians. Some 1.5 million residents remain in the city and worst-case forecasts see up to a million being uprooted, according to the United Nations.

U.N. aid agencies said the fighting has so far forced about 9,000 to flee their homes. But Lise Grande, the U.N. humanitarian coordinator for Iraq, told Reuters that the United Nations expects a mass exodus from Mosul, perhaps within the next few days.

In the worst case scenario, Grande said it was also possible that Daesh fighters who have controlled Mosul for more than two years could resort to “rudimentary chemical weapons” to hold back the impending assault.

A commander said the CTS advance on Mosul was pausing to allow other military units to make similar progress and consolidate the front before pushing further more into the city.

The Iraqi force attacking Mosul is 30,000-strong, supported by U.S. special forces and under American, French and British air cover. The number of insurgents dug in the city is estimated at 5,000 to 6,000 by the Iraqi military.

About 90 Daesh-held villages and towns around Mosul have been retaken so far into the offensive, according to statements from the army. The distance from the front lines to the city ranges from just a couple of kilometers in the east, to 30 kilometers in the south.

In Khazna, one of the villages recaptured Monday by the CTS, some of the fighting appeared to have gone from house to house, leaving smoked out buildings with their contents turned upside down, a Reuters correspondent said. A disabled Humvee and the remnants of a car bomb could be seen on a desert path.

CTS snipers hid on rooftops at the edge of village keeping watch over the desert areas extending to Mosul.

Although CTS is a government unit, many of its Humvees fly the Shiite flags of Iraq’s majority community. Such a display could antagonize Sunnis who make up most of the population in Ninevah province.Paramilitary forces were also massing near the battlefield to open a western front they say will aim to retake the town of Tal Afar and cut off routes to neighboring Syria for Daesh fighters escaping Mosul.

Thousands of men from the Popular Mobilization, a paramilitary umbrella group dominated by Tehran-backed Shiite militias, were preparing for a push to the west.

The Popular Mobilization mission will be to “fully isolate Mosul from Syria,” Jawad al-Tulaibawi, spokesman for the Asaib Ahl al-Haq militia, said.

Seeking to relieve pressure on their forces controlling the northern Iraqi city, Daesh fighters who have waged counterattacks across the country battled Iraqi troops in the desert town of Al-Rutbah, 450 kilometers to the southwest.

Daesh attacked Al-Rutbah Sunday and has been fighting since then for the town, which lies on the main highway running west from Baghdad, close to the borders with Jordan and Syria.

The militants expanded the area of Al-Rutbah under their control to about half Monday overnight, forcing the government to send reinforcements.

The Daesh attack on Al-Rutbah came after an assault on the Kurdish-held oil city of Kirkuk last week.