THE assault on the city of Fallujah by Iraqi troops and Iranian-backed militiamen is adding to the humanitarian catastrophe being experienced in the country, and increasing sectarian tension throughout the Middle East. The aim of the attack on Fallujah, 40 miles west of Baghdad, is to defeat Islamic State (IS) forces that have been in control of the city since January 2014.

The international refugee agency UNHCR has reported that up to 4000 civilians have fled from Fallujah, adding to the 3.2 million Iraqis who are homeless. At the same time, as many as 50,000 civilians remain in the city. The UN said that IS is preventing many of them from leaving and is using them as human shields.

The UNHCR said that it had received reports of casualties among civilians in the centre of Fallujah as a result of heavy shelling, including seven members of one family. “Conditions for those trapped in the city are dire,” it said, and there were “reports of several starvation-related deaths amid food shortages. Families have had to rely on unsafe water sources, including drainage water from irrigation canals. Health facilities and medications are unavailable.”

Two other issues of concern for Iraq are inherent in the assault on Fallujah. The first is that IS is reacting to the military pressure on it there by carrying out suicide attacks both on Iraqi army units in the region and on civilian targets in Baghdad and elsewhere; dozens of people are being killed and injured. The number of attacks across the country has risen sharply over recent days.

Second, there is concern among the predominantly Sunni Muslim population of Fallujah that the defeat of IS would result in the city’s being taken over by Shia militiamen (members of the Hashd al-Shaabi, or “popular volunteer force”), who enjoy Iranian support.

Fallujah is in Anbar province, the Sunni heartland of Iraq, where IS emerged — largely in reaction to the marginalisation of Sunnis by the Shia-dominated government of the former prime minister Nouri al-Maliki. Islamic militants were joined by former Iraqi army officers to form IS. The Iraqi army was disbanded by the post-2003 United States-led transition authorities because of its close association with the Ba’ath Party of Saddam Hussein — a move that contributed directly to the breakdown of law and order in the country.

While most Iraqi Sunnis are uncomfortable with the ideals and methods of IS, they also abhor the prospect of Shia militiamen taking control of their towns and cities. Sunnis throughout Iraq were shocked to learn that the leader of the Quds Force of the Iranian Revolution Guards Corps, Qassem Soleimani, visited Hashd al-Shaabi fighters around Fallujah as the assault began. Saudi Arabia, which is leading Sunni Arab states’ campaign to block Shia expansion in the Middle East, said that Mr Soleimani’s presence in Iraq was totally unacceptable.

So, against the background of rising Sunni-Shia tension throughout the Middle East, the attack on Fallujah, whether or not it proves to be successful, will inevitably raise the levels of sectarian hatred in Iraq and elsewhere.