The federal government in Baghdad first imposed the air blockade in September after Iraqi Kurdistan voted overwhelmingly for independence in a non-binding referendum rejected as illegal by the central government.

It was extended in December for two months and was to run until February 28 but the authorities decided to renew it for three months, the official said.

"We have been informed by the civil aviation authority in Baghdad that the ban on international flights to and from Arbil and Sulaimaniyah airports has been extended until the end of May," he said.

"Only internal flights are authorised."

A spokesman for Prime Minister Haider al-Abadi's office confirmed the ban was extended.

"No date had been set to lift the ban," Saad al-Hadithi told AFP.

"It will depend on the transfer of the airport's administration to the federal government and when that will be done the ban will be lifted," he added.

According to Hadithi, "progress" has been made during negotiations involving Kurdish and federal government officials on several issues, including customs, passports and visas.

"But the issue of the control of security at the airports has not been solved yet, although there is a will to reach a solution to this problem," he added.

Before the controversial September vote on independence, the authorities in Kurdistan were in charge of all these issues but after the poll that angered Baghdad, the federal government demanded to take control.

Since the flight ban went into force, all Kurdistan-bound international flights have been rerouted to Baghdad, which has also imposed entry visas to foreigners wishing to visit the Kurdish region.

The flight ban was part of a battery of penalties inflicted on the Kurds as Baghdad sought to nullify the poll, with federal forces also seizing disputed oil-rich regions.