The UN Security Council on Thursday warned that a referendum on independence by Iraq's Kurdistan region was potentially destabilizing, adding its weight to international opposition to the vote.

In a unanimous statement, the 15-member council said the referendum planned for Monday could hinder efforts to help refugees return home and weaken the military campaign against the Islamic State group.

The move heightened pressure on Iraqi Kurd leaders to call off the vote after Turkey, Iran and Iraq urged them to abandon the plan that is also opposed by the United States.

Council members "expressed concern over the potentially destabilizing impact of the Kurdistan regional government's plans to unilaterally hold a referendum next week," said the statement.

"The planned referendum is scheduled to be held while counter-ISIL (Daesh) operations -- in which Kurdish forces have played a critical role -- are ongoing," it added.

The council urged "dialogue and compromise" to address differences between the Iraqi government and the regional authorities.

Iraqi Kurds will vote on September 25 in the non-binding referendum on whether to declare independence in a region that has already been autonomous since the aftermath of the 1991 Gulf War.

The United States has warned it may not be able to help Iraq's Kurds negotiate a better deal with the Iraqi government if they go ahead with an independence vote.

UN Secretary-General Antonio Guterres on Sunday urged the Iraqi Kurds to scrap the referendum and offered UN help to negotiate a new political deal between Baghdad and the Kurds.

UN envoy to Iraq, Jan Kubis, told Iraqi Kurdish leader Massud Barzani last week that the United Nations was ready to broker negotiations between the Kurds and Baghdad, according to a document obtained by AFP.

The negotiations would aim to reach a deal within two or three years on the "principles and arrangements" for future relations between Baghdad and the Kurdish region, the document said.

In return, Barzani's administration would agree to postpone the referendum at least until the end of negotiations.