"From tomorrow (Sunday) we will start a big aerial defence manoeuvre that will last for five days ... covering an area of some 600,000 square kilometres in north, southwestern Iran and parts of south and central Iran," Brigadier General Ahmad Mighani, the army air defence chief was quoted by the Fars news agency as saying.

The aim of the exercises is to thwart the aerial threat posed by an imaginary enemy on Iran's nuclear facilities -- from reconnaissance to actual assault -- and also to improve cooperation among different units.

"Due to the threats against our nuclear facilities it is our duty to defend out nation's vital facilities and thus this manoeuvre covers Bushehr, Fars, Isfahan, Tehran and western provinces," he added.

"Our unit will be in charge of the manoeuvre but there will be units from Revolutionary Guards and the Basij (militia)," he added.

Iran's still unoperational nuclear plant is in the southern Bushehr province and its other nuclear sites, namely uranium enrichment plants, are in Isfahan and near Tehran.

Iran's enrichment work is at the centre of fears about its atomic ambition as the process which makes nuclear fuel can also be used to make atomic bombs. Tehran insists that its nuclear programme is entirely peaceful.

Washington and Israel have never ruled out a military strike against Iran's nuclear facilities.

Tehran has often held defence war games and has boasted advances in military capabilities in a bid to show its readiness to counter any military threats over its disputed nuclear programme.

Tehran which says its nuclear programme is a peaceful drive to generate electricity, has threatened to hit back at Israel and US interests in the region if it is attacked.

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