BAGHDAD: The United Nations said it will 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 late Wednesday 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, Masoud 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 ISIS's 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.

Baghdad says such a referendum cannot be determined by a single party and that it will lead to more problems. Turkey and Iran, which have large and sometimes restive Kurdish minorities, have also expressed strong displeasure over the vote.

Some Iraqi Kurds, mainly the opposition party Gorran, have criticized Barzani, whose term in office expired in 2015 prompting a political limbo, and demanded that the referendum should be held after parliamentary and presidential polls.

With a population of about 5 million, Iraq's Kurdish region already enjoys a high degree of autonomy, including its own parliament and armed forces. Since 2003 U.S.-led invasion that toppled Saddam Hussein, relations with the central government in Baghdad have become strained over a range of issues, including the sharing of oil revenues and control of some areas, such as the oil-rich city of Kirkuk.

IS militants routed the Iraqi security forces and took control of much of the country's north in 2014. Since then, the Kurdish peshmerga forces have retaken large chunks of IS-held territory, including Kirkuk, leading to more tensions with Baghdad.