Iran on Monday launched an air defence exercise a general said was aimed at optimising its deterrent capabilities as well as sending a "strong warning" to those threatening it with military strikes.

The start of the manoeuvres, originally scheduled for early October but postponed without an official explanation, was announced on the website of the Revolutionary Guards, sepahnews.com.

They drill comes against a backdrop of growing tension in Gulf, but appears unconnected to an incident last week when two Iranian fighter jets fired on an unarmed US drone.

Some 8,000 troops drawn from the ranks of the Guards, the army and the Basij militia are participating in the drill, which will span four days and cover an area stretching 850,000 square kilometres (328,000 square miles) in Iran's eastern regions, according to media reports.

Various missile and artillery systems as well as fighter jets and bombers will be used in the exercise, they said.

The units will also test "fixed, mobile and tactical radar devices and tactical and airborne electronic surveillance systems," according to Brigadier General Farzad Esmaili, head of the Guards' air defence command.

Iran frequently conducts missile tests and manoeuvres to underline its military muscle should it come under external threat.

Such exercises have multiplied in recent years amid growing tensions with the West and Israeli threats of possible air strikes on Iran's nuclear facilities.

"For those who are thinking of aggression against the Islamic Republic of Iran, the exercise should be seen as a strong warning," drills spokesman Brigadier General Shahrokh Shahram told Iran's English-language Press TV.

He did not elaborate.

The drone incident in the Gulf occurred on November 1, made public by the Pentagon a week later, heightening tension between Iran and the US amid a mounting crisis over Tehran's nuclear programme.

Iran said the unarmed Predator drone had entered its airspace and that its jets fired warning shots.

The Pentagon denied the drone had entered Iranian airspace and warned of a stronger response should there be a repeat of such an incident.