DUBAI/ISTANBUL/ERBIL, Iraq (Reuters) – Iran halted flights to and from Kurdish regions in northern Iraq on Sunday in retaliation to a plan by the autonomous Kurdistan Regional Government (KRG) to hold a referendum on independence. It also started wargames at the Kurdish border.

The air embargo is the first concrete retaliatory measure against Monday’s Kurdish referendum which is rejected by the government in Baghdad and by Iraq’s powerful neighbors, Iran and Turkey.

Iranian authorities stopped air traffic to the international airports of Erbil and Sulaimaniya, in Iraqi Kurdistan, upon a request from Baghdad, Fars News Agency said.

Tehran and Ankara fear the spread of separatism to their own Kurds. Iran also supports Shi‘ite groups who have been ruling or holding key security and government positions in Iraq since the 2003 U.S-led invasion which toppled Saddam Hussein.

Turkey, meanwhile, said on Sunday its aircraft launched strikes against Kurdistan Workers Party (PKK) targets in northern Iraq’s Gara region on Saturday after spotting militants preparing to attack Turkish military outposts on the border.

”Turkey will never ever tolerate any status change or any new formations on its southern borders,“ Turkish Prime Minister Binali Yildirim said. ”The KRG will be primarily responsible for the probable developments after this referendum.

The KRG has resisted calls to delay the referendum by the United Nations, the United States and Britain who fear it could further destabilize the region.

The vote, expected to result in a comfortable “yes” to independence, is not binding and is meant to give the KRG a legitimate mandate to negotiate the secession of the autonomous region with Baghdad and the neighboring countries.

The KRG says the vote acknowledges the Kurds’ crucial contribution confronting Islamic State after it overwhelmed the Iraqi army in 2014 and seized control of a third of Iraq.

Iranian State broadcaster IRIB said military drills, part of annual events held in Iran to mark the beginning of the 1980-1988 war with Iraq, were launched in the Oshnavieh border region.

The war games will include artillery, armored and airborne units, it said.

Clashes with Iranian Kurdish militant groups based in Iraq are fairly common in the border area.

INSURGENCY

On Saturday, Turkish warplanes destroyed gun positions, caves and shelters used by PKK militants, a military statement from Ankara said. Turkey’s air force frequently carries out such air strikes against the PKK in northern Iraq, where its commanders are based.

Turkey’s parliament voted on Saturday to extend by a year a mandate authorizing the deployment of Turkish troops in Iraq and Syria.

The PKK launched an insurgency in 1984. More than 40,000 people have been killed in the conflict. It is designated a terrorist group by Turkey, the United States and the European Union.

The U.S. embassy in Iraq cautioned its citizens that there may be unrest during a referendum, especially in territories disputed between the KRG and the central government like the multi-ethnic oil-rich region of Kirkuk.

Three Kurdish Peshmerga fighters were killed and five wounded on Saturday when an explosive device blew up near their vehicle south Kirkuk, security sources said.

The explosion happened in Daquq, a region bordering Islamic State-held areas, the sources said.

Islamic State’s “caliphate” effectively collapsed in July, when a U.S.-backed Iraqi offensive, in which the Peshmerga took part, captured their stronghold Mosul, in northern Iraq.

The group continues to control a pocket west of Kirkuk and a stretch alongside the Syrian border and inside Syria.