IRBIL, Iraq/BAGHDAD: Iraqi forces said they were about to complete the encirclement of the stronghold of Daesh (ISIS) in the Old City of Mosul, after taking control of a neighboring district Thursday. Iraq’s military said it had captured Bab Sinjar, north of the historic, densely populated district where the militants launched their cross-border “caliphate” in 2014.

Government forces and their allies still have to take full control of Medical City, a complex of hospitals further north along the bank of the Tigris, to enclose the militant enclave.

The offensive to retake the northern city started in October with air and ground support from a U.S.-led international coalition.

Iraqi government forces retook eastern Mosul in January then a month later began the offensive on the western side where about 200,000 civilians remain trapped behind Daesh lines.

The fall of Mosul would, in effect, mark the end of the Iraqi half of the “caliphate” that Daesh leader Abu Bakr al-Baghdadi declared in a speech from a historic mosque in the Old City.

About 800,000 people, more than a third of the prewar population of Mosul, have already fled, seeking refuge with friends and relatives or in camps.

Meanwhile, the United Nations said it would not be “engaged in any way or form” in the process surrounding the independence referendum in Iraq’s northern semi-autonomous Kurdish region planned for September.

The statement by the U.N. special mission to Iraq, or UNAMI, released Thursday could cast doubts on the credibility of the vote, which has already sparked wide criticism from the central government in Baghdad and several regional and Western nations.

Last week, the president of the Kurdish region, Massoud Barzani, said the vote, slated for Sept. 25, will determine whether the Kurdish region would secede from Iraq.

The balloting is to be held in three governorates that make up the Kurdish region but also in areas that are contested by both the Kurds and the central government. Those disputed areas have been under the Kurds’ control since the 2014 Daesh onslaught in western and northern Iraq and the withdrawal of security forces from these areas.

The UNAMI statement did not say why it was distancing itself from the referendum, but added that it “seeks to rectify inaccurate news reports that UNAMI will oversee, support or observe” the vote. UNAMI “has no intention to be engaged in any way or form” with the referendum, it concluded.

Iraq’s Kurds said the referendum on independence will go ahead despite warnings from Western powers that a vote in favor of secession could trigger conflict with Baghdad at a time when the war against Daesh is not yet won.

The Kurds are playing a major role in the U.S.-backed campaign to defeat Daesh, the ultra-hard-line Sunni group that overran about a third of Iraq three years ago and also controls parts of Syria.