Iraq's prime minister has given the country's Kurdish region until Friday to hand over airports to federal authorities or face a flight ban.
Haider al-Abadi's ultimatum on Tuesday came the day after Iraq's Kurds held a referendum on independence that has been roundly denounced by Baghdad and Iraq's neighbours.
Mr Al-Abadi says the ban would exclude humanitarian and other "urgent" flights.
The Kurds have their own regional government, parliament, armed forces and airports in Iraq's three northern provinces, where they have enjoyed constitutional autonomy for more than a decade.
They control disputed territories outside those provinces that are also claimed by Baghdad.
The referendum is not binding and will not immediately lead to independence, but it has increased tensions in the region.
Turkey has threatened to intervene militarily and is holding joint military drills with Iraq on the border.
The Arab League called on Iraqis to renounce their differences and open comprehensive dialogue to avoid clashes following the referendum.
Ahmed Aboul-Gheit, chief of the Cairo-based pan-Arab organisation, said in a statement: "It is still possible to contain the repercussions of this step if all concerned parties exercise wisdom and responsibility and conduct themselves inside the parameters of the Iraqi state."
The interests of Iraq, he added, "will be best served in the framework of a unified, federal and democratic Iraq".
While the referendum is not binding and not expected to immediately lead to independence, it has shaken the region, eliciting condemnations from Iraq's neighbours as well as the United States and the United Nations.