Turkey on Thursday warned Iraqi Kurdish leaders that a planned independence referendum this month would “have a cost”, as Ankara refused to budge in its opposition to the poll.

The non-binding poll set for September 25 faces strong opposition from Turkey as well as from Iran, which fear it will stoke separatist aspirations among their own sizeable Kurdish minorities.

Iraq's parliament on Tuesday voted down the plan in a session that prompted a walkout by Kurdish lawmakers.

The Turkish foreign ministry warned in a statement that the Iraqi Kurdish leaders' call for a referendum was “worrying”.

The Iraqi Kurdish government's “insistence... despite all friendly advice will definitely have a cost”, the ministry said, advising it to turn back from an “erroneous approach.”

The ministry said it welcomed the decision made by the Iraqi parliament, adding that its vote was a “clear indicator of importance attached to Iraq's political unity and territorial integrity”.

Turkish presidential spokesman Ibrahim Kalin urged the Iraqi Kurdish government to “return from this wrong decision as soon as possible.”

He warned the move would push Iraqi Kurdistan into “bigger isolation.” Kalin said there was no other country, or international organisation “other than Israel” that backed the referendum bid.

Israeli Prime Minister Benjamin Netanyahu on Tuesday backed the Kurds' aspirations for a state of their own, without specifically referring to northern Iraq.

“While Israel rejects terror in any form, it supports the legitimate efforts of the Kurdish people to attain a state of its own,” a statement from Israeli prime minister's office said.

Israel's apparent support for the referendum has been roundly condemned in pro-government Turkish media.

Kurds, a people with a separate language and distinct culture from Arabs and Turks, live in parts of Turkey, Syria, Iraq and Iran. Turkey has the largest proportion of ethnic Kurds, who make up around a quarter of its population of 80 million.

Turkey — which for over three decades has battled the outlawed Kurdistan Workers' Party (PKK) in its southeast — is strictly opposed to any move to a Kurdish state anywhere in the region.

Ankara is also deeply troubled by aspirations of some Kurds in Syria for an autonomous region on its border and considers the Syrian Kurdish Kurdish Peoples' Protection Units (YPG) to be a terror group.

Kalin on Thursday said: “There will absolutely be consequences for this referendum decision,” without elaborating further.

Critics of the vote, including the United States and the European Union and even some members of Iraq's 5.5 million-strong Kurdish minority, say it could distract from the fight against Islamic State militants.