Backed by US airstrikes, artillery and special forces “advisors,” Iraqi troops began storming Mosul’s crowded Old City, where the United Nations estimates that some 150,000 civilians are trapped under the siege.

Iraqi commanders have issued triumphalist statements hailing the offensive as the beginning of the end for the Islamic State of Iraq and Syria (ISIS), which took control of Iraq’s second-largest city after government troops melted away in the face of their advance in June 2014.

“This is the last chapter” in the battle for Mosul, Lt. Gen. Abdul Ghani al-Asadi, the commander of the Counter Terrorism Service (CTS), the elite US-trained unit that has borne the brunt of the fighting, told the media Sunday. He warned that he expects a “vicious and tough fight.”

How long this “last chapter” will last is by no means clear. Some commanders have predicted that it will take at least a month to retake the area. US-backed Iraqi forces began their siege of Mosul eight months ago. Since then, thousands of Iraqi civilians have died under US bombs, rockets and shells. The UN has confirmed the killing of 230 civilians in western Mosul during the last two weeks alone, undoubtedly a significant undercount of the real death toll. The rest of the population has been reduced to desperate conditions, without adequate food, water or medical aid.

This final stage of the battle may well prove the bloodiest. The Old City is the most densely populated area of Mosul, with narrow alleyways that will make an advance by infantry troops difficult.

The International Rescue Committee, which is coordinating aid to the civilian population, warned that it expects a sharp rise in bloodshed. “With its narrow and winding streets, Iraqi forces will be even more reliant on airstrikes despite the difficulty in identifying civilians sheltering in buildings and the increased risk of civilians being used as human shields by ISIS fighters,” said Nora Love, the IRC’s acting country director.

Love added that “the buildings of the old town are particularly vulnerable to collapse even if they aren’t directly targeted.”

The launching of the siege of the Old Town was preceded by an intense bombardment by US and allied warplanes, together with an intense artillery bombardment beginning at midnight.

The Washington Post quoted an Iraqi officer as reporting that the offensive began with the early morning firing of three TOS-1 thermobaric rockets into an area near a school. The so-called “fuel-air” weapons disperse a cloud of flammable liquid into the air around the target, and then ignite it. The results are horrific, generating a more powerful explosion and shockwave than conventional missiles and consuming all of the oxygen in the area. They can kill everything in a 3,000 square-foot area, with victims dying from the intense pressure of the blast or suffocating as their lungs rupture as a result of the air vacuum.

The use of these terrifying weapons against densely populated neighborhoods follows the earlier confirmation that the US military has attacked Mosul with white phosphorous shells, which are banned in populated areas. The incendiary chemical weapons ignite human flesh on contact, burning it to the bone.

The use of these weapons and the mounting number of civilian casualties is evidence of the US military implementing what US Secretary of Defense James Mattis described last month as “annihilation tactics” in the anti-ISIS campaign. “Civilian casualties are a fact of life in this sort of situation,” Mattis, a recently retired Marine Corps general who led the murderous sieges against Fallujah in 2004, commented at the time.

US warplanes have dropped leaflets on Mosul’s Old Town urging residents to flee. While those who do face the threat of dying in US bombardments or being killed in the crossfire, the Pentagon is clearly creating the groundwork for arguing that civilians being slaughtered are either “human shields” or ISIS diehards.

Even if the US and Iraqi government forces succeed in retaking all of Mosul, after reducing most of this ancient city on the banks of the Tigris River to rubble, it will by no means spell an end to the savage conflict that was unleashed by the US invasion in 2003.

Sectarian divisions, manipulated by the US occupation as part of a divide-and-rule strategy, will only be exacerbated by the retaking of Mosul. The city fell to ISIS in the first place because of the bitter resentment of its Sunni majority population against the Shia-dominated government and army. Now this same army is assuming control, backed by Shia sectarian militias.

Huge numbers of people will remain homeless and in desperate need. More than a year after the so-called liberation of Ramadi from ISIS control—after 80 percent of the city’s buildings were damaged or destroyed—only 60 percent of those displaced have been able to return.

Moreover, Washington has no intention of withdrawing its troops from Iraq. It was reported early last month that the Pentagon had entered negotiations with the government of Prime Minister Haider al-Abadi on a proposal that would maintain a permanent US troop presence in Iraq. The plan calls for thousands of US troops to remain in the county, deployed at five separate bases, including on the Iraqi-Syrian border.

The pretext for this continued military presence is that of preventing a resurgence of ISIS in Iraq. The real aim, however, is to further US geostrategic aims in the region, which include removing Iran as an obstacle to the imposition of unchallenged American hegemony over the oil-rich Middle East.

The Trump administration has deliberately stoked a confrontation between the Sunni regimes led by the Saudi monarchy and predominantly Shiite Iran. In Iraq, this conflict poses the threat of reigniting a bloody civil war, with or without ISIS.

This threat was underscored by remarks made over the weekend by Prime Minister Abadi and earlier in the week by his vice president, Iyad Allawi, a former CIA asset and one-time US-installed prime minister.

Abadi stressed that he would not allow Iraq to be turned into a battlefield between the US and Iran or a launching pad for attacks on Iran. “If we are given the rule of the entire world and promised free reconstruction, we will not engage in hostility toward Iran,” he said.

Speaking earlier in the week during a visit to Egypt, Allawi echoed Washington and the Saudi regime, accusing Iran of interfering in parliamentary elections set for next year and charging that both Iran and Qatar are seeking to “split Iraq into a Sunni region in exchange for a Shia region.”