Masoud Barzani, president of Iraqi Kurdistan, was last night defiant over his decision to hold a controversial referendum on independence, even as its neighbour Iran mounted pressure by closing its airspace and launching military drills on the border.

Tehran announced on Sunday it was blocking all flights to and from Kurdistan at the request of ally Iraq, which has described the secession vote as “unconstitutional” and warned that it could fan the flames of tensions in the Middle East.

Some five million Kurds will go to the polls today in the three provinces that have since 2003 formed the autonomous region of Kurdistan, but also in territories disputed with Baghdad such as the oil-rich province of Kirkuk.

Mr Barzani, a 71-year-old guerilla leader-turned-politician who enjoys something of a cult of personality in Kurdistan, has mustered huge popular support for the vote.

The streets of Erbil, Kurdistan’s capital, are festooned with red, white and green Kurdish flags and large crowds holding nightly rallies.

The Kurds - more than 30 million people spread across Iraq, Turkey, Iran and Syria - have long sought a state of their own. The result seems a foregone conclusion.